TRAFFIC SIGNALS AND SIGNALISED ROUNDABOUTS

Transcription

1 TRAFFIC SIGNALS AND SIGNALISED ROUNDABOUTS Ian Routledge -

2 OBJECTIVE OF PRESENTATION I have 32 years experience of traffic signal and systems design, implementation, operation and maintenance There are a number of issues that I know are not always picked up during the RSA process Objective of this presentation is to try to raise awareness of some of these issues I am not attempting to pick up every aspect but focus on those important to me - sometimes presentation goes beyond scope of road safety audits I understand that a RSA is an independent review of the design to ensure all safety issues have been addressed making recommendations when necessary

3 STRUCTURE OF THE PRESENTATION Comment on the life cycle of signals and what this means for safety Look at some key areas Signal layouts, particularly signal heads Pedestrian facilities particularly Puffins Right turning traffic Traffic speed and detection Discuss issues at signalised roundabouts Consider construction issues Ask if we are looking in the right places for risks

4 LIFE CYCLE SAFETY CONCERNS Concept development/outline design Sometimes problems start here Poor option selection, poor modelling etc Almost unbuildable schemes with little scope to change Traffic signals community talking to transport planners Detail Design Lack of expertise in signals design and associated civils Factory and site acceptance testing FAT/SAT/Commissioning - lack of expertise FATs not being undertaken Construction an increasing concern Operation and maintenance is there the resources and expertise available

5 LAYOUT Layout fundamental to safety and efficiency Adequate lanes and radii Use turning circles to ensure clearance But turning circle assessments seem to vary considerably Pedestrian crossings Keep crossings off radii Balance between desire line and safety Some key dimensions Stopline to studs 3m for safety reasons! Poles max 500mm from tactile paving but minimum of 500mm from kerb, 750mm minimum if signal heads Many poor designs a result of expanding the layout Radii for supersized vehicles and lack of use of islands

6 Keep power pillar close but not abutting controller

7 SIGNAL HEADS Drivers should always be able to see a head when approaching or stopped at stopline - in any lane 3 lane approach central lane a problem if no splitter island And if one of the lanes is a bus lane? Primary heads Hatching out of nearside lane offsets primary heads so is this a safety risk? Secondary heads Never considered at initial design stage Maximum 50m from stopline to secondary Closely associated secondary heads should be cut away as primary hoods so can be seen safety issue Obsession with double heads / tall poles

8 Signal head effectively set back 3m behind hard shoulder safety risk? Signal head effectively set back 3m behind hatching safety risk?

9 Do we really need this many heads and the high pole?

10 PEDESTRIANS/TOUCANS Pedestrian/Toucan/Equestrian facilities can be Traditional farside Nearside (Puffin) facilities with pedestrian detection Research has shown when well implemented that Puffins Reduce accident rates overall by 21% More efficient Average cycle time reductions of 20% Benefits for those with poor sight or learning difficulties So why are farside facilities being installed? The preferred stagger is this really important? See through a problem at all pedestrian crossings but especially so at splitter islands Minimised if required 3m separation between crossings is achieved

11 PUFFIN FACILITIES Nearside displays Make pedestrians look at approaching traffic not away High level repeaters and narrow field of view available Puffin on crossing detection Clearance period extended if pedestrians present between minimum and maximum (L/1.2 or greater if required) Cheap, reliable, and effective and controller safety feature Should be always used except at very narrow crossings Kerbside detection Cancels demands if pedestrians depart but not needed with parallel pedestrian phases that run with main road Need to specify a safety feature Expensive and technology still improving but can be very effective

12 PUFFIN CHECKLIST Nearside displays Between pedestrians and nearest approaching traffic Correctly aligned - see-through? High level repeaters required? Puffin on crossing pedestrian detection On all but the narrowest crossings Easy to check by observation Kerbside pedestrian detection Not installed when phase runs in parallel with main road Demand cancelled when pedestrian leaves Safety feature operation demand entered when kerbside detector does not detect a pedestrian does not cancel

13 No separation of crossing Crossing on radius Stopline 1m from studs

14 RIGHT TURNING TRAFFIC In gaps as long as flows and speed are low Right turn green arrow gives robustness Call/cancel loop Some drivers do not move forward use stopline loop If a conflicting right turn at cross roads use closely associated secondary heads for manoeuvre without arrow Separately signalled right turns often used High speed road To facilitate pedestrian crossings If use a left filter from side road a with a right turn into the side road The filter has to be terminated by a full green If filter always runs so will the side road demand dependent

15 SPEEDS High speed roads 85 percentile greater than 35mph Guidance requires Double or triple speed discrimination Speed assessment MOVA MOVA Need to adjust intergreens UTC and SCOOT should have speed discrimination when speeds are high Maintainability an issue because of numbers of loops Or just increase the intergreens and forget about the dilemma zone a safety risk?

16 TRAFFIC DETECTION Loops Very effective but prone to damage and fail safe Use for speed discrimination/assessment with XYZ loops Use for call/cancel and specific applications Carriageway loop boxes to minimise of damage Above ground Very effective and low cost different technologies Can get MVDs that are lane specific Move is to all above ground where possible Above ground detector demands and extends Above ground stopline detection to replace stopline loop

17 SIGNALISED ROUNDABOUTS Signalised roundabouts Large motorway interchanges Small 25m diameter Staging strategy two stage operation Circulatory and entry are the two stages Smaller sites run staging anticlockwise and hold flows on entries until required Key is managing the queues Strategies Timetabled plans (CLF) MOVA and linked MOVA FT UTC or SCOOT

18 SIGNALISED ROUNDABOUTS If high speeds need SA/SD or MOVA Queues On off slips can cause safety problems On circulatory cause lock up Anti-gridlock strategy detects queues on critical links and flushes out the circulatory Signal heads See though a particular issue Use tunnel hoods or twist hoods through 90 degrees Controlled switch off so circulatory first then entry Part time operation Timetabled but also queue activated

19 CONSTRUCTION ISSUES Recent experience has shown that shown civils works often fail to comply with design requirements Across all aspects Ducting and chambers Road markings Crossing location/alignment Poles etc Mistakes are rarely corrected even when identified on site during commissioning and RSAs Safety built into designs is being compromised How do we put this right? Lack of site staff knowledge/interest The information supplied, e.g. Setting out data?

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21 500mm offset? Studs miss dropped kerb Pole 500mm from line of studs?

22 Nearly! But a 1.8m wide crossing is nearly 2.4m

23 RISKS How many risks does poor construction create? Do the following issues create safety risks? Timings not updated? Failing to repair loop detectors? MOVA not properly validated/maintained? SCOOT not properly validated/maintained? Is unnecessary congestion an unnecessary risk? Is implementing complex strategies that cannot be maintained a safety risk? For some authorities this includes MOVA and SCOOT Is failing to recognise limitations a risk? Consultants and Local authorities Is an RSA commenting on detail signal issues without detail signal knowledge a safety risk?

24 Any queries in future call or