Traffic Efficiency Guidelines for Temporary Traffic Management

Transcription

1 Traffic Efficiency Guidelines for Temporary Traffic Manaement Version 3.1 Final July

2 Contents 1 Glossary of Terms Settin the Scene COPTTM TMP Principle Traffic Volumes Hourly Profiles, Peak Periods, Directions and Traffic Counts Rules of Thumb to Use When Limited or No Traffic Count Data are Available Traffic Count Sources Local road traffic counts State Hihway traffic counts Mere Capacities Typical Mere Capacity Factors Influencin Mere Capacity Multi lane Roads Flow Profile Speed Flow Density Relationships Volumes Above 1500 vph/lane Speeds Below 15 km/hr Speeds reater than 15 km/hr with less than 1500 vph/lane Stop / Go Capacity Road Closures and Detours Worksites Adjacent to an Intersection Worksites close to an intersection Impact of a Worksite on Traffic Sinals Impact of Traffic Sinals on a Worksite Appendices A Useful Equations 14 B Speed Flow Capacity 15 C Stop / Go Capacity 16 2

3 1 Glossary of Terms AADT COPTTM HPMV km/hr NZTA RCA SIDRA STMS TMP TSL TTM vph Annual Averae Daily Traffic Code of Practice for Temporary Traffic Manaement Hih Productivity Motor Vehicle kilometres per hour New Zealand Transport Aency Road Controllin Authority Sinalised & Unsinalised Intersection Desin and Research Aid Site Traffic Manaement Supervisor Traffic Manaement Plan Temporary Speed Limit Temporary Traffic Manaement vehicles per hour 3

4 2 Settin the Scene Road works have the potential to disrupt traffic flow and result in delays to road users. To ensure network efficiency, queuin at road works should be minimised, to prevent motorist frustration and improve safety. These uidelines are aimed at the desiners of TMPs, to help them to minimise network impacts when desinin Temporary Traffic Manaement Plans. These uidelines provide information that can be used to help optimise worksites to ensure minimal disruption to a network. The base expectation is that existin traffic movements will be maintained wherever possible. These uidelines are intended to add to COPTTM Section C COPTTM TMP Principle Temporary Traffic Manaement (TTM) shall be carried out to avoid, or at least minimise, inconvenience and delay to road users whilst still providin safe conditions for both the road users and those carryin out the work activity. Traffic volume capacity predictions included in this document may need to be reduced if: The road is rouh or unsealed, The horizontal eometry restricts speeds to less than 40 km/hr, The proportion of heavy vehicles exceeds 12%. Every TTM situation is unique and these uidelines may not suit all situations. 4

5 3 Traffic Volumes 3.1 Hourly Profiles, Peak Periods, Directions and Traffic Counts The weekday mornin peak period is typically between 7am and 9am. The evenin peak period is typically from 4pm until 6pm, but may run until 7pm in larer cities like Auckland, Wellinton and Christchurch. Typically, one direction has more traffic volume than the other durin these peak periods. There are shoulder periods each side of the peak periods when traffic volumes are buildin or reducin. The interpeak period is typically between 9am and 4pm thouh there is often an increase in flow between 2pm and 4pm (Fi. 1). Weekends and public holidays often have a sinle peak, but this usually has a loner duration which typically lasts from 10am until 4pm. FIGURE 1. Typical Daily Traffic Volume Profile. 3.2 Rules of Thumb to Use When Limited or No Traffic Count Data are Available The mornin or evenin peak periods (1 hour flows) can be assumed to be 10% of the AADT flow. Countin traffic volumes for 15 minutes in a typical mornin peak, and multiplyin by 40 will provide a rouh approximation of the AADT flow. For weekend traffic counts, it can be assumed that the maximum hourly flow is equivalent to the weekday inter-peak (2-4pm) traffic flow. However, on some major routes the weekend maximum hourly traffic flow can be equivalent to the mornin peak traffic flow. 3.3 Traffic Count Sources Historical traffic count data provides uidance when decidin on the proposed TTM methodoloy, but do not uarantee that the methodoloy and deployment timeframes will be practical on site. The STMS must verify actual traffic volumes prior 5

6 to deployment of the TMP, to confirm that the impact on the network will be as expected. Traffic volumes on a public holiday or durin school holidays differ from those found on typical workin or weekend days. Traffic volumes on holiday start and end days are often hiher than on days durin the holiday period. These differences occur in both the peak traffic volumes and the daily profile. Care must be taken when desinin TMP s for these days. It is recommended that TMP desiners contact their local RCA Traffic Enineer for uidance. There is an NZTA State Hihway Traffic Monitorin System which contains detailed directional counts by quarter hour. In addition some sites are counted 365 days a year, which can be useful when lookin for annual trends. There are times of the year which enerally experience lower traffic volumes than others e.. school holidays Local road traffic counts RCA s hold their traffic count data in different ways and on different systems. Links to data for some of the major RCA s are iven below. Please contact your local RCA for more data. Auckland Hamilton Taurana To be located Wellinton To be located Christchurch ount/index.aspx In Christchurch, iven the chanes to traffic patterns around the city in the postearthquake environment, actual traffic counts may differ from the historical data. Use count data from a 2011 or 2012 count even if you need to use an adjacent site. Dunedin To be located State Hihway traffic counts 6

7 4 Mere Capacities To minimise delays and queuin in mere situations, the actual volume of traffic at a site must be taken into account. 4.1 Typical Mere Capacity The most straiht-forward mere (two lanes into one) typically operates efficiently at volumes of up to 1300 vehicles per hour (vph). Hiher traffic volumes lead to sinificant slowin, queuin and potential tail-backs (flow breakdown) extendin back alon the approach, which can have sinificant neative effects on safety and efficiency in other parts of the roadin network. It is recommended that when traffic volumes in one direction are in excess of 1300 vph, a minimum of two lanes should be maintained (Fi. 2) FIGURE 2. Example of Flow Breakdown. Fiure 2 shows that as traffic volumes exceed 1300 vph, vehicle speeds rapidly decrease. Vehicle speeds only recover once traffic volumes fall below 1300 vph. A fiure of 1300 vph should be used as a uideline for the volume at which the mere capacity breaks down. The TMP desiner must ascertain what is appropriate for the site, dependin on the site-specific factors present. It is recommended that TMP desiners contact their local RCA Traffic Enineer for uidance. 7

8 4.2 Factors Influencin Mere Capacity Site-specific factors affect the actual capacity of a mere operation. Important factors include: Geometry Siht distance Mere lenths Upstream / downstream operations Site complexity Flow profile Environmental factors. If all of these factors are at optimal levels, mere operations can achieve a capacity of 1600 vph, but this is rare. In most situations, some factors are not optimised and the mere capacity is consequently lower. A ood example is a curved alinment, with minimum mere lenths and relatively close upstream or downstream priority-controlled intersections. In this situation, the environment is more demandin on road users and the mere capacity is likely to be quite a lot lower than 1300 vph. 4.3 Multi lane Roads For multi-lane roads, multiples of the uideline 1300 vph capacity can be used to predict if impacts on traffic flow will occur. For example, when merin from three lanes into two, a mere operation can typically operate efficiently up to 2600 vph. A typical mere capacity fiure of 1300 vph is enerally reliable in a rane of speed environments. However, the TMP desiner must ascertain the appropriate volume at each site. It is recommended that TMP desiners contact their local RCA Traffic Enineer for uidance if uncertain. 4.4 Flow Profile The flow profile must be considered when decidin the start and end times for a TMP. Generally, settin out a mere at a worksite should only commence once the flows are below the estimated mere capacity. Any consequent delays and queuin will be shortlived, as the approach volume is reducin. This means that site set-up should typically occur after the peak periods. It can be danerous to maintain a mere operation as traffic volumes are climbin towards the estimated mere capacity (e.. as the mornin peak period is beinnin). If delays and queuin bein before the TTM is uplifted, queues can continue throuhout the day, until after the evenin peak period. The impact on network safety and efficiency can be sinificant, and may result in intense media, political and stakeholder pressure on the RCA and contractors involved. The components of a TMP that require mere operations (e.. mere taper; mobile operations that close a lane), must be fully uplifted well before traffic volumes climb to the mere capacity. The estimated mere capacity (and consequent TMP start and end times) can be verified on site and refined if necessary. The STMS should count traffic volumes durin the closure to identify when traffic volumes start to increase towards the mere capacity. The STMS must allow sufficient time in the upliftin methodoloy to clear the lanes before the capacity is reached. 8

9 5 Speed Flow Density Relationships To minimise delays when reducin the speed limit, the volume of traffic per lane must be taken into account. Fiure 3 has been developed to help determine if the flow of traffic will break down at a site with a proposed decrease in speed, which may cause sinificant queuin and delays. FIGURE 3. Relationship Between Vehicle Speed and Flow Breakdown. (Refer to Appendix A for the detailed calculation equation) The shaded area below the solid line in Fiure 3 shows the speed at which a total breakdown in flow will occur: Veritcal solid line - At hih speeds, the maximum lane capacity is 1800vph/lane, based on a 2 second spacin between vehicles (the 2 second rule). Slopin solid line - Drivers need a minimum spacin between vehicles of around 20m (front bumper to front bumper) for traffic to flow smoothly, if the spacin drops below this then traffic flow will break down. At 1800vph/lane, the spacin drops below 20m when the speed drops below 36km/h. As the speed is reduced below 36km/h, the vehicle throuhput has to reduce as well to maintain the 20m spacin necessary for smooth traffic flow. Horizonal solid line Experience has shown that at speeds lower than 15km/h the traffic flow breaks down. COPTTM Section C4.1.4 states that a Temporary Speed Limit must be: At least 20 km/hr less than the existin permanently azetted speed limit In multiples of 10 km/hr Appropriate to the condition of the road Not lower than 20 km/hr. It is recommended that Temporary Speed Limits be increased or removed whenever a worksite is not bein worked on, if site conditions allow. 9

10 5.1 Volumes Above 1500 vph/lane While the capacity of a sinle lane in theory is 1800 vph, in reality traffic flows can breakdown at much lower traffic volumes, or may not break down till as hih as 2200 vph/lane. Site-specific factors such as side-friction (resultin in rubber neckin ), intersections (roads or motorway ramps), and the number of sideways shifts required alon the worksite can all affect the actual capacity of a site. COPTTM Section C indicates that interrupted traffic flows and queuin are likely to occur at about 1500 vph, and caution is recommended whenever traffic flows are approachin or exceedin 1500 vph. The TMP desiner must ascertain what is appropriate for the site, dependin on the site-specific factors present (e.. the requirement for an anti-awkin screen etc). It is recommended that TMP desiners contact their local RCA Traffic Enineer for uidance if uncertain Speeds Below 15 km/hr Experience with Rollin Blocks has shown that it is not possible for a line of queued vehicles to travel at speeds lower than 15 km/hr without the traffic flow breakin down. Therefore, the solid line in Fiure 3 has been levelled off at this speed. However, to avoid flow breakdown, it is recommended that a minimum speed of 20 km/hr or more should be maintained Speeds reater than 15 km/hr with less than 1500 vph/lane This is the traffic speed and volume conditions occur at most sites. There is no need for any special consideration should these conditions exist. 10

11 6 Stop / Go Capacity COPTTM (Section C10.2) states that Stop / Go operations shall not be used where two-way traffic flow can be maintained past a worksite. To minimise delays under Stop / Go control, the optimum Go time should be determined and applied to deliver maximum capacity. Fiure 4 has been developed to help determine the optimum Go time. The followin assumptions have been made in developin this chart: the speed throuh road works that require manual traffic control is 30 km/hr (this equates to 500 meters in one minute) the departure rate of a vehicle in a queue is 1.8 sec/vehicle all of the vehicles that arrive whilst the Stop control is operatin are able to depart in the followin Go time. FIGURE 4. Determination of Stop / Go Times. (Refer to Appendix A for the detailed calculation equation) Manual Traffic Controllers usin Stop / Go paddles are considered to be more responsive to chanes in traffic patterns than portable traffic lihts or other options. If it is intended to use Stop / Go operations at a worksite near a set of traffic sinals, please refer to Section 8. 11

12 7 Road Closures and Detours Road closures resultin in a detour need to be manaed efficiently and effectively. The followin factors should be considered: Can an alternative methodoloy be used to maintain traffic movements? For example: stain the works differently keepin a sinle lane operational throuh the worksite detourin only a sinle direction of traffic niht work that can take advantae of reduced traffic volumes The diverted traffic volumes need to be determined. The proposed detour routes need to be assessed: This may be able to be completed on an intersection by intersection basis, or network modellin may be required Can the normal volume plus the detoured volume be accommodated at each intersection on the detour route? Is the proposed detour route sensible? (It should match motorists expected detour route.) Would you want/expect to drive the detour? Check for the presence of HPMV s and Over Dimension vehicles. These can be either heavy (reater than 44 tonne) or loner / wider / hiher than normal, makin turnin manoeuvres more difficult. These types of vehicles are enerally restricted to a permitted route from Point A to Point B, so detourin them will require permit chanes which is often a very substantial task, but can be done. HPMV operators often have a perception that their vehicles are overweiht and therefore cannot travel where there are weiht restrictions on brides. However, this may be permissible. Please consult your local RCA for further information. If any detours are required, the TMP desiner must contact the local RCA Traffic Enineer to aree the appropriateness of the detour and if any modellin and analysis are required. 12

13 8 Worksites Adjacent to an Intersection Worksites close to an intersection Particular care needs to be taken with any site that will be located near an intersection, especially if there is a roundabout or traffic sinals. The uidelines outlined in this document must be used to ascertain if queuin will occur throuh the intersection. If this is the case, the TMP desiner must consider appropriate mitiation for the intersection. It is recommended that the TMP desiner contact their local RCA Traffic Enineer for uidance Impact of a Worksite on Traffic Sinals If a worksite is within 250 metres of an intersection with traffic sinals, and it will chane the operation of the intersection, then the TMP may disrupt traffic flow, cause additional queuin, and possibly have wider network effects. The followin factors should be carefully considered in desinin the TMP: chanin the turnin movements allowed from any lane closin lanes shortenin lanes placin plant and equipment near an intersection where they may be detected by the traffic sinal detection loops (e.. a temporary fence, sin, container or any vehicle). Please contact your local RCA to aree the appropriate level of analysis required (which may include modellin) to determine the efficiency impacts of your proposed TMP. Software such as SIDRA are useful tools for micro-modellin traffic flow throuh intersections. Adjustments to the operation of an intersection (e.. reen times, sinal phases) may need to be desined into the TMP to maintain network efficiency. The RCA welcomes requests to chane the operation of a set of traffic sinals if it improves the efficiency of the network. However, the operation of traffic sinals is complex and not all requests may be considered appropriate or be implemented Impact of Traffic Sinals on a Worksite If a worksite is reater than 250 meters away from an intersection with traffic sinals, it is unlikely that the worksite will affect the traffic sinals. However the traffic sinals may have an impact on the operation of the worksite. The effect on a worksite from traffic sinals is most important when the site uses a Stop / Go operation, because the traffic sinals will cause traffic to arrive at the worksite in roups (platoons). The Stop / Go reen times will therefore need to be closely linked to the traffic sinal s reen times. 13

14 Appendix A: Useful Equations Speed-Flow-Density Relationship Equation The Speed-Flow-Density relationship equation is shown below. speed _( km / hour) 1000 _( metres / km) Flow _( vehicles / hour) spacin _( metres / vehicle) In the rane of speeds 15-36kph a minimum spacin of 20m should be assumed. This equation does not apply at less than 15 kph For reater than 36kph, the spacin should be calculated from a 2 second ap which requires the followin equation (two seconds at 100 kph is 55.6m.) speed _( km / hour) 1000 _( metres / km) spacin _( metres / vehicle) spacin _(sec onds) 3600 _(sec onds / hour) Optimum Go Time Equation The hourly traffic flow in each direction throuh a manually stop-o controlled site can be approximated by takin the number of vehicles passin throuh the site on a sinle reen phase, and dividin by the total cycle time. Considerin vehicles travellin up the pae: 1. Go Time 2. All Red 3. Stop Time 4. All Red t t rr t r t rr Total Cycle Time = t + t rr + t r + t rr 14

15 Number of vehicles in a cycle = All Red, t rr = Traffic Flow = DepartureRate x t Lenth of Site, L Speed throuh site, V Number of vehicles movin in each cycle Total cycle time DepartureRate x t t +L/V + t r + L/V If we assume Stop Time t r and Go Time t are the same, then we can rearrane the equation for Go Time, t. Go Time, t = 2 x TrafficFlow x L/V DepartureRate 2 x TrafficFlow NOTE UNITS: TrafficFlow - vehicles/second Lenth, L - metres Speed throuh site, V - metres/second (use 8.33m/s, which is 30km/h) DepartureRate - vehicles/seconds (use 0.56) Queue Lenth at Manually Controlled Stop-Go Sites Considerin vehicles travellin up the pae: 1. Go Time 2. All Red 3. Stop Time 4. All Red t t rr t r t rr 15

16 The queue that has been buildin up while the STOP sin has been showin beins to clear out as soon as the GO sin is shown (vehicles 1,2 and 3 in the diaram). However it doesn't clear immediately. Each vehicle takes off a short time after the one before it takes off (assumed to be 1.8 seconds). While vehicles are leavin the queue from the front, other vehicles are arrivin and joinin the queue at the back (vehicle 4). The queue is only completely cleared once the last vehicle (vehicle 4) leaves, allowin arrivin vehicles to proceed throuh without stoppin (vehicle 5). The maximum queue lenth is the distance to the back of the last stopped vehicle (vehicle 4). This lenth is equal to the number of vehicles arrivin in one complete cycle, multiplied by the averae lenth of each vehicle. Likely maximum number of vehicles queuin = TrafficFlow x t + t + t + t rr r rr = Flow x 2(t + trr) (assume t = tr) (because t = Flow x 2(t + L/V) rr = L/V as Averae lenth of vehicle = Lenth Liht x % Liht + Lenth Heavy x % Heavy = 7m x 90% + 28m x 10% = 9.1m Maximum queue lenth = Number of vehicles x averae lenth of vehicle = Flow x 2(t + L/V) x 9.1m NOTE UNITS: TrafficFlow Lenth, L Speed throuh site, V Go time t - vehicles/second - metres - metres/second (use 8.33m/s, which is 30km/h) -seconds 16

17 Appendix B: Speed Flow Capacity 17

18 Appendix C: Stop / Go Capacity 18