GLASGOW CITY COUNCIL PEOPLE TRIP ASSESSMENT

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1 GLASGOW CITY COUNCIL PEOPLE TRIP ASSESSMENT An analysis of benefits and drawbacks By JMP Consulting Note This report is an independent analysis of Glasgow City Council s People Trip Assessment method. It is not the result of any research undertaken by TRICS. Introduction The importance of addressing accessibility is now an important element of Transportation Assessments. Accessibility refers to the distance that people must travel to access goods, services and participate in activities (such as employment or social, retail facilities etc) and the transport options that can be used to reach them. Access is the ultimate goal of most transportation, excepting the small portion of travel in which movement is an end in itself. In order to address access issues Glasgow City Council (GCC) have developed an modelling tool People Trip Assessment which covers not only Glasgow but is promoted by GCC for use throughout Scotland. The aim of this report is to highlight the benefits and drawbacks of using the People Trip Assessment (PTA) method, it is not intended to be used as a how to manual, rather it provides a broad overview of the method. The report offers a brief summary of the People Trip Assessment method, why it is used and a critique of the benefits, limitations and pitfalls of the method. In order to identify these benefits and limitations two case studies have been included, one for a residential development and one for an employment based PTA. Finally, having reviewed the method a series of conclusions have been made. Glasgow City Council s People Trip Assessment The Glasgow City Council People Trip Assessment (PTA) method is based principally on Gravity Modelling, a tried and tested method which has been used in transportation studies for the past 30 years. Where the Glasgow City Council method differs from previous gravity modelling is the attempted introduction of a multi-modal element into the model (public transport, walking and cycling). The Glasgow City Council PTA method is a distribution tool and not an assignment tool, comprising three separate Excel Spreadsheets, one each for Residential developments, Employment developments and Visitors/ Customers to developments. The Glasgow City Council PTA Method in Practice For developments within Glasgow City Council boundaries, People Trip Assessments (PTA) are now an expected norm for assessing site accessibility. The approach has been developed by Glasgow City Council (GCC) to address the emerging requirements of national planning policy guidance. The PTA approach is a method for determining the potential number of residual vehicle trips generated by a development, taking account of the accessibility of other modes of travel. The PTA technique identifies the maximum possible sustainable mode share of a site, implying that some form of deterrence to use of the car, or encouragement to use alternatives

2 to the car are required to achieve the mode share calculated through the application of this process. The accessibility methodology employed is based upon a previous study undertaken by GCC termed the Oatlands Transportation Assessment and determines the number of person trips generated by the development and the resulting modes of travel. In order to undertake this process the following stages are undertaken: 1. Establishment of current relevant council wards from boundary ward maps available on Local Government Boundary Commission for Scotland website ( 2. Establishment of council wards having centroids within a 20km radius survey area of the proposed development site. This distance is a function of the method but could be altered if required. Distances to the ward centroids from the proposed development site are measured from the appropriate Ordnance Survey maps, following the lines of the existing local and trunk road network. 3. Identification of the level of generation from each identified ward as a percentage of the total population of the agreed survey area. 4. Establishing available public transport routes which afford access to the proposed site, and plotting on to an area wide plan. All public transport links, which afford access to the site, were established to enable services that pass through a particular ward to be easily identified. 5. Assessment of accessibility of public transport, walking and cycling with regard to access to the site from each ward. To identify the level of sustainable transport available all potential pedestrian, cycle and bus routes have been identified. Where the routes have been identified detailed information on the level of frequency for bus routes has been examined to identify the level of service available to the trip within that area. 6. To identify the level of modal split a number of criteria have been identified for different accessibility ratings. This identifies the level of service criteria which has to be met before a certain rating can be put on an area. The ratings are on a simple scale of 1 (very good) to 5 (very poor). For public transport the rating related to the frequency of service. For walking and cycling the rating related to journey times at 6kph for walking and 18kph for cycling. For each ward area the best accessibility rating was chosen. 7. To identify the level of private car trips to the development a projected modal share, again has been applied to the appropriate accessibility rating. A rating of 1 was given a modal split of 10% by car: 90% by sustainable transport, 2 30% car: 70% sustainable, 3 50% car: 50% sustainable, 4 70% car: 30% sustainable, 5 90% car: 10% sustainable. The anticipated number of car trips from each postcode area was then assessed by applying the modal split to the number of staff in the postcode area. The various splits and ranges have been developed solely by GCC without consultation with external transportation practitioners. As a result it is unclear how the figures were derived. The assessment identifies the principal direction of travel in the AM peak. For example, residential equates to generation while employment equates to attraction. In practice, we never identify the trip generation, we need another stage which says identification of total trip generation as a function of land use. In residential developments this equates to the number of economically active etc. General Spreadsheet Instructions The PTA spreadsheets are used to determine travel patterns specifically to or from a development site. This may be either the total generation for an office development or the employee portion of a retail development etc.

3 It must be noted that this particular method is not designed for City Centre or specialist developments which may have an attraction from a much wider area such as a major hospital. Adaptations to the method for such developments can be agreed at the initial scoping stage. The tables within the spreadsheets are automated as far as possible and will produce results if the instructions are followed to the letter. The columns in red must be completed in each part of the spreadsheet and those in blue may be manually altered from the automatic result but only if accompanied by valid reasoning. The columns in black must not be altered. The spreadsheets should be used initially to assess the development "in the raw". Should this initial assessment indicate that some enhancement to the sustainable transport provision is required, the sheet should then be used again to show the estimated result of any enhancement. Both sets of sheets should be submitted with the eventual Transport Assessment. Ideally the spreadsheet covering the initial assessment should be submitted for agreement in advance of any scoping meeting in order to assist the Engineers/ Planners to come to a rapid decision on the required scope of the eventual T.A. in order to save time and effort. Within the Population Statistics table the population data is standardised and based on information derived from the 2001 population census. The local authority ward boundaries are those in use at that date. The distance from the site should be taken from the building entrance to the demographic centroid of the ward. This distance should be measured to the nearest 0.1km along the shortest suitable traffic route for distances up to 7.5km in order to allow the acceptable automatic calculation of pedestrian and cycle accessibility ratings. For distances greater than 7.5km the measurements may be rounded up to the nearest 1km and for those greater than 20 km, to the nearest 10km. The direction of travel is a feature associated specifically with Glasgow City related developments and need not be adopted for other uses. The direction is not necessarily the compass direction from the site to the ward. It is the direction taken on leaving the site or at the first significant choice point from the site and should be chosen to allow direct analysis of the various routes from the site. The column for the %age distribution and the tables at the bottom of the sheet are automated and are for interest rather than analysis. The Employment Statistics table data is standardised using the information from the Office for National Statistics 2001 ABI data. However, the Office of National Statistics have not yet updated its database to the current (1997) ward boundaries thus the ward information relates to the 1992 wards. In many cases this results in the practitioner searching historic maps, or find a name which closely resembles the ward name. Residential Spreadsheet The following example is derived from a People Trip Assessment for a residential development in the Hyndland area of Glasgow. In order to maintain client confidentiality all references to the actual site have been removed. The first stage is identifying accessibility by non car based modes of walk, cycle and public transport which is rated in accordance with user attraction or disincentive as appropriate. The GCC method does not, however, consider any of the recognised incentives/ disincentives to using non-car modes and is based purely on a simplistic distance, or in the case of public transport frequency basis. Attractions are accessibility, frequency, reliability, speed and comfort and disincentives are cost, undesirable company, overcrowding, mode changes and any lack of attraction factors.

4 The rating system within the model assumes that the accessibility from the site is such that the public transport access point does not require a walk of greater that 2min or 200m from the development and that the waiting area is provided with a shelter and is well lit. If the walk distance is not met then the public transport rating is treated as if a change of mode is required, such a change being dealt with by determining the rating for the walk time from the site to the interchange point and adding this to the pt rating (e.g. a ten minute walk to a train station would add two points to the rating for the rail journey alone). It may appear simplistic to assume that a 10 minute walk would make a difference to the choice of travel mode, however, National Travel Survey statistics indicate that this may account for a significant number of car trips. These statistics illustrate that cars are used for 18 per cent of trips under 1 mile and for 61 per cent of trips of between 1 and 2 miles. The proportion of short trips made by car is slowly increasing. The rating for each stage of the journey is assessed and the ratings summed. The general assumption within the model is that the public transport journey is reasonably direct. However, it must be noted that the public transport ratings are on the basis that the service runs at the appropriate frequency throughout the working day. The rating may be reduced by 1 (assuming it is greater than 1) for rail travel, to reflect the additional attraction of rail as a mode of transport, provided no change of mode other than walking or cycling is involved. In the Accessibility table, the Public Transport Accessibility column is the only one requiring any input as the Pedestrian and Cycle ratings are automatically calculated and based on measurements from the proposed development to ward centroid. However these may be adjusted downwards if a suitable off-road short-cut is available and currently well used or is committed to be provided by the developer. Conversely they could be adjusted upwards if the chosen route involves steep gradients or other disincentives to pedestrians or cyclists. If in doubt the journey should be travelled by an average person to determine the time taken and hence the rating to be given. The final stage is to enter the number of proposed dwellings within the proposed development and then insert the anticipated economic activity rate. Person movements, modal splits and car commutes to each ward are then automatically calculated and summated dependant on the direction of travel from the site. However, the method ignores the possibility of economic activity outwith the peak hour, and of non-employment related travel occurring during that period, for example, the trip to school. The method implies that these two factors are balanced, which is absolute speculation. There are difficulties with the default values and these relate to inflexibility on the part of a Local Authority to consider alternatives for the method to be useful. It must therefore, be adaptable to the unique circumstances of the development and its surroundings. It must be noted that the model is not calibrated for the particular area in which the development is located. The model could be calibrated against every multi-modal TRICS survey to determine for these areas the total trip generation accords with the application of this method. In addition, it must be noted that the spreadsheet does not take account of economically active individuals who travel outwith the peak AM period, trips associated with the economically inactive, nor is there any justification or validation that people will leave an area in which they reside. Particular care is required when considering economic activity. The default value is unlikely to reflect the specific characteristics of the area under consideration. This is particularly relevant in city locations where employment activity per household could vary significantly by ward. The method output is a projection of likely numbers of people who will use cars. No detailed output of sustainable modes is available, however, the columns already exist within the accessibility table to take the model to the next level and become a true multi modal model, and it seems strange that there is no attempt to extrapolate likely numbers of individuals who will use public transport or will walk and/ or cycle.

5 Assessment of Development Impact For comparison purposes and to assist with contra-peak trip generation estimates, trip generation rates for either the residential development or employment related development must be extracted from the TRICS Database (Version 2004(b)) database. Peak hour data from TRICS has been extracted to determine the trip generation rates indicated by Table 1. For a residential development, this information relates to the number of observed arrivals and departures as a ratio against the number of housing units. Table 1 applies these rates to the proposed development content to provide an overall estimate of the number of vehicle trips or where appropriate, people trips associated with the proposed development in the AM and PM peak hours. The PTA only calculates the trip in the AM peak, with the remaining values taken from TRICS output. Table 1. TRICS Data TRIP RATE for Land Use 03 - RESIDENTIAL/K - MIXED PRIVATE HOUSING Calculation Factor: 1 HHOLDS ARRIVALS DEPARTURES TOTALS No. Ave. Trip No. Ave. Trip No. Ave. Trip Time Range Days HHOLDS Rate Days HHOLDS Rate Days HHOLDS Rate 00:00-01: :00-02: :00-03: :00-04: :00-05: :00-06: :00-07: :00-08: :00-09: :00-10: :00-11: :00-12: :00-13: :00-14: :00-15: :00-16: :00-17: :00-18: :00-19: :00-20: :00-21: :00-22: :00-23: :00-24: Daily Trip Rates:

6 Employment Spreadsheet The employment (and visitor/ customer) spreadsheet differs from the residential spreadsheet at the final stage where the total number of people to be employed on the site is entered into the box at the bottom of the results table. The number of car commutes from each ward during the peak period will then be displayed together with the direction of travel to the site. The relationship between inflow and outflow and between different periods should then be applied using profiles derived from the appropriate TRICS database. The assessment of the number of employees should relate to the size and type of the development and be the maximum the development could sustain even if this is greater than is currently intended. As a rule of thumb, for office developments an employment level of 1 person / 25m 2-1 / 35m 2 floor area could be anticipated, for class 4/5 developments a level of 1 person / 20m 2 site area would be acceptable. Any assessment utilising employment levels lower or higher than these estimates would require justification of the use of such figures. The following example of the employment spreadsheet is derived from the assessment of a Class 4 development in Govan, Glasgow. It should be noted that the Use Classes in Scotland differ from those in England. The Employment Spreadsheet was used to determine the trip generation and distribution of a proposed Class 4 development in Glasgow and the associated traffic utilising the GCC People trip Assessment method, specifically, based on the percentage draw from the council wards identified as falling within a 20km radius of the site utilising the existing local and strategic road network. GCC advised that for a Class 4 development, such as the development highlighted in this section, the estimated number of employees on the site should be based on a density rate of 1 employee per 20m 2 of GFA. The 14,000m 2 development site is to consist of a mixture of laboratory and office accommodation supporting in the region of 600 to 750 employees on its final completion. It has been assumed that the development would operate as conventional office space and laboratory, whereby the majority of employees are anticipated to arrive in the morning and depart in the evening, although there are likely to be some trips in the non-peak. Based on a total number of 700 employees, the People Trip Assessment determined a total of 274 anticipated car trips. The GCC Employment Spreadsheet, although determining the total number of anticipated car trips associated with the development, does not determine the AM and PM peak period arrival and departure profiles. In order to determine the AM and PM peak period arrival and departure profiles, TRICS 2004(a) was used. The arrival and departure profiles determined from TRICS are indicated in Table 2 below.

7 Table 2. People Trip Generation Profiles Business Class 4 Business 14,000 sq.m Generation Rates (per 100sq.m) In Out Total Weekday AM Peak Weekday PM Peak Source: TRICS 2004(a) Table 2 above indicates an AM peak arrival and departure profile of 93% and 7% respectively and a PM peak arrival and departure profile of 9% and 91% respectively. For the purpose of this assessment, considering the similarity between the AM and PM arrival and departure profiles above, the AM peak arrival and departure profile of 93% and 7% was adopted and reversed for the PM peak. The resultant AM and PM peak anticipated car trip profiles are therefore as indicated in Table 3. Table 3. Anticipated Car Trip Profiles Class 4 Business Generation Rates 14,000 sq.m In Out Total Weekday AM Peak Weekday PM Peak Percentage Distribution to/from a Proposed Development With regard to the distribution to and from a proposed development site from the identified council wards, the Glasgow City Council People Trip Assessment Spreadsheet incorporates built in percentage population weighting factors, based on the distance of the identified council ward from the proposed development site, that are automatically applied to the individual council ward populations as part of the overall calculation process of determining the total number of anticipated people trips attributable to the proposed development. With regard to the Residential Spreadsheet, the population weighting factors are applied as follows. The assumption is that 905 of trips generated from a residential development in the AM peak will travel to wards within 10km of the site. Of the council wards identified as falling within a distance banding of 10km to 30km from the proposed residential development, it is assumed that 10% of their respective total population employed within the ward will originate from the proposed residential development. With regard to the Employment Spreadsheet, the population weighting factors are applied as follows.

8 Of the council wards identified as falling within a distance banding of less than 3km from the proposed development, it is assumed that 60% of their respective total economically active population will be attracted to the proposed development; Of the council wards identified as falling within a distance banding of 3km to 5km from the proposed development, it is assumed that 10% of their respective total economically active population will be attracted to the proposed development; Of the council wards identified as falling within a distance banding of 5km to 10km from the proposed development, it is assumed that 20% of their respective total economically active population will be attracted to the proposed development; Of the council wards identified as falling within a distance banding of 10km to 20km from the proposed development, it is assumed that 10% of their respective total economically active population will be attracted to the proposed development. The Glasgow City Council People Trip Assessment Spreadsheet, both Employment and Residential, has been set up in such a way as to clearly discourage the user altering the above mentioned weighting factors. Although the above weighting factors would be applicable in some circumstances, proposed development sites often, by nature and location, differ considerably. There may be instances where you have an employment based proposed development, that by nature, will require to employ a highly skilled workforce however, is located in a low skill area therefore, it would be reasonable to assume that considerably less than 60% of the economically active population of the identified wards within 3km of the proposed development site would be likely to make up the potential workforce. In addition to the above, irrespective of whether the proposed development is employment or residential based, if the location of the site is rural, it would be reasonable to assume that the travel distances would be greater, and that a significantly higher percentage of trips would originate from, and travel to, council wards located out with 10km of the proposed development. In conclusion, it is clear that there is an argument to be made for tailoring the spreadsheet to allow the user to adjust the percentage population weighting factors to more realistic values based on the particular nature and location of the proposed development. Any proposed alteration to the default values would obviously require agreement with the appropriate local authority.

9 Visitor/Customer Spreadsheet Although the visitor/ customer spreadsheet is very similar to the employment spreadsheet there are subtle differences. The spreadsheet is used to determine travel patterns by customers or visitors to a development site. Although similar to the employee spreadsheet, additional information is required as to the perceived attraction of the development. A local facility obviously attracts visitors from a far smaller catchment area than a major site. In the case of, for example, a regional hospital, the catchment area is known and thus only those wards within the catchment need be taken into account. Similarly a major retail development will have a known catchment area determined from the Retail Impact Assessment, which, incidentally, must be available prior to any meaningful scoping meeting. The major difference between these types of development in terms of traffic generation is that in the former case the generation/population may be taken as being constant over the entire catchment area whereas in the latter case it will vary dependant on the difference in distances and ease of accessibility between competing facilities and the customer, i.e. a gravity model. In this latter case, however the task may be simplified by constructing isochrones between the development and all competing sites and making the assumption that the customer population crossing from the development's catchment area to a competing site will be equal to the movement in the opposite direction. On this basis therefore it would be acceptable to again assume the generation/population ratio is constant throughout the area. In such cases it is unlikely that the "cross boundary" traffic will be greater than 5% of the pre-existing traffic flow thus further analysis would be unnecessary. The one exception to these assumptions would be in the case where the proposed development is so close to an existing facility that it may be taken as being complementary rather than competitive. In this case the combination of proposed and existing should be compared with similar developments rather than the proposed alone. Similar reasoning may be used for more local developments such as community centres. The main difference between this spreadsheet and the employment spreadsheet is thus the assumption that the generation in this case is spread equally over the catchment area. The ratings for walking and cycling have also been adjusted to reflect the different circumstances in being a customer rather than an employee and the total adult population is used rather than just the economically active. Conclusion The Glasgow City Council People Trip Assessment method is not unique, other more complex methods exist for determining levels of accessibility to a particular development site. Its main benefit is its relative simplicity, and the potential it has for potential enhancement to the spreadsheets which will allow it to link with off the shelf computer programs thus providing a geographical representation of potential trip distribution. However, one of the main criticisms of the Glasgow City Council People Trip Assessment methodology is its lack of validation. There is very little information relating to the validation process with which the PTA method has been subjected. As such, any claim of validation made for the method must be documented with appropriate research evidence, because validation involves the accumulation of evidence to provide a sound basis for the proposed method. Validity is therefore extremely important to ensure the PTA method measures what it is supposed to measure. In addition, inflexibility on the part of a Local Authority relating to the input figures can be one of the principal weaknesses of the method. For the method to be useful it must be capable of adapting to the unique circumstances of the development and its surroundings. From experience, different individuals have produced different results for the same development using the Glasgow City Council PTA spreadsheet. Had it been validated the method would be capable of producing similar results irrespective of user input. Further

10 clarification on input requirements must therefore be included before a comprehensive validation exercise is carried out. The PTA spreadsheet can therefore be validated using the following methods: 1. Validated by comparison to other methods or software. One or more existing method or software products may be used for comparison. This form of validation is performed when the answers cannot be reasonably calculated by hand. 2. Validated by comparison to textbook examples. Data and output from respected textbooks are used for comparison. This form of validation is usually performed in combination with the previous method. 3. It may also be appropriate to validate against survey data. Therefore, by applying the method to sites where TRICS multi-modal surveys has occurred it may be an opportunity to validate the method. Because of the simplicity of the PTA method it does have limitations and constraints. Some of these are nothing more than irritants, others are more significant affecting the performance of the spreadsheet and the potential trip generation results itself. The method does not take into consideration route attractiveness. Within the PTA spreadsheet it is assumed that because a cycling/ pedestrian route is available then it will be used. It does not take into account route safety or hazards, only the shortest distance between two points is considered. Assumptions regarding public transport, especially for multi-modal trips, can be misleading. General attractiveness of using public transport will relate to journey time and waiting time which is not represented. The method does have potential to produce a multi-modal model, however, at present it is merely a car counter with no breakdown of anticipated walkers, cyclist or public transport users. This would be the next logical step in the development of the method. One particular area which is weak is the multi-modal element of the method. It should be borne in mind that it is still only a gravity model which evaluates potential car trips. The results are still car orientated i.e. percentage of trips expected by car. However, there is no breakdown on potential number of trips by foot, bicycle and bus. Developing this particular area would appear to be the next natural step to improving the overall usability of the PTA spreadsheets. The method relies on the measurement of distances between ward centres with stepped changes which can produce incongruous variations for very minor changes in distance. In addition, the PTA method only predicts total Peak AM trips, In (employment) and Out (residential). In order to make full use of the spreadsheet TRICS data must be applied to determine peak am and pm trips (in and out). If the PTA method is to be used in a Transportation Assessment which supports a particular development, this information is a requirement for predicting trip rates. It would be very easy to write the methodology off as not being robust enough to be used in Transport Assessment. However, current alternatives are limited. The benefit of the PTA is that is simple to use and has the potential to be improved. In addition, it must be borne in mind that the methodology is based on a tried and tested method i.e. gravity models, which have served the transportation industry well for the past years. The principal advance of the PTA method is the attempt to incorporate a multi-modal element into the method. Admittedly there are usability issues associated with the method, however, these can be ironed out making this a cost effective and systematic model.

11 One of the main reason for the development of the PTA method in Scotland is a lack of TRICS data, particularly multi-modal data. While the PTA method may have its limitations it does allow all sites, irrespective of location to be assessed. However, there is still a need for TRICS data when calculating peak am/pm IN and OUT car movements. Until the number of multi-modal sites increases, then there will continue to be a requirement for the Glasgow City Council PTA method.