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High risk intersections - making sense of safe systems in practice

High risk intersections - making sense of safe systems in practice. Tim Hughes – National safety engineer. Safer journeys action plan. Improve high-risk intersections

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High risk intersections - making sense of safe systems in practice

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  1. High risk intersections - making sense of safe systems in practice Tim Hughes – National safety engineer

  2. Safer journeys action plan • Improve high-risk intersections • We will use the High Risk Intersection Guide to identify and target the 100 highest-risk intersections to address by 2020. • In 2013 a high-risk intersection programme will be developed and launched. • Over 2014/15 the following will be delivered: • By September 2014 solutions will be developed for at least 30 high-risk intersections. • By June 2015 at least 20 high-risk intersections will be improved as per agreed solutions.

  3. High Risk Intersections - Top 100 list • 40 are at traffic signals • 37 of these are urban signals / 47 urban total • Only 3 are rural signals. • However: we also have a top 700 list based on collective risk and there will be a similar number on personal risk. • Some of these may be better value for money to fix than the top 100. HRIG helps you to identify and prioritise.

  4. The Safer Journeys Safe System Vision A safe road system increasingly free of death and serious injury

  5. Safe Speed Thresholds • Roads with possible conflicts between • vehicles and unprotected users 30-40 km/h • Intersections with possible • side-on conflicts between vehicles 50 km/h • Roads with possible frontal • conflicts between vehicles 70 km/h • Roads with no likelihood of frontal • or side-on conflicts between road users 100 km/h

  6. The challenge of a safe system • The focus on deaths and serious injuries • Identifying high risk locations • Crash types that result in deaths and serious injuries (DSIs) • How do countermeasures affect crash severity • Crash prediction models and crash severity / casualties • Prioritising on saving DSIs • Safety Audit

  7. Structure of HRIG

  8. Severity by Side impact speed

  9. Severity by Speed limit

  10. Severity by Speed limit

  11. Main crash types - urban

  12. Main crash types - rural

  13. What is a HRI? – collective risk • High-risk intersections are intersections with a higher than normal risk that someone will die or be seriously injured in the future. • Using recent F&S history is like chasing lightning strikes. • To get a better picture: more years of data • Use all injury data to estimate DSIs – gives better prediction. • Because of small crash numbers at any one intersection, a high-risk intersection is only tentatively defined in a short list, and needs to be confirmed by further analysis: • Risks are measured using estimated DSIs, calculated as: • Collective risk: estimated number of DSI equivalents • Threshold 1.1 estimated DSI equivalents in 5 years. • 700 intersections – 2.5% of intersections high and medium high

  14. Personal risk • Where there are enough crashes (4) to permit a valid calculation, personal risk – or risk of DSI per vehicle using the intersection can be assessed. We have also set thresholds for these. • We cannot perform this analysis globally at present because we do not have automatic access to the traffic flow data, but there is now a database with 25,000 intersections in GIS. • We have used this data to set thresholds for high personal risk. • Similar number to high and medium high collective risk with little overlap.

  15. What is a high risk intersection?

  16. Treatment Philosophy Strategy

  17. LoSS and Transformation potential • Once we have the flow data we can also use crash prediction models to compare the reported crashes with those that we would normally expect for an intersection of that type with that amount of traffic. We call this the Level of Safety Service (LoSS). • We can use a similar method to compare the potential for improvement by changing to a different form or control type.

  18. Level of Safety Service: Urban 4 leg signals

  19. What is a high risk intersection? - Auckland

  20. Comparing intersection types

  21. Comparing intersection types

  22. Comparing intersection types

  23. Countermeasures – What have we learnt? • Pedestrians: • Where pedestrians cross a traffic stream – vulnerable due to traffic speed. • Rarely a red running issue - pedestrian compliance - longer cycle times worsen pedestrian safety. Pedestrian optimised? • Where traffic is turning, typically speeds are slower – but still severe if a heavy vehicle is involved turning at lights. • Half of urban pedestrian and cyclist deaths involve a heavy vehicle. • Pedestrians early start?

  24. Countermeasures – What have we learnt? • Rural intersections: • Priority cross roads and T-junctions are by far the worst – very high risk and high severity. • Roundabouts best - if exits clear zoned. • Rural signals need careful design, phasing, detection and clear zones - but can be lower risk –especially at T-junctions .

  25. Countermeasures – clear zones – at intersections

  26. How are we responding to the challenge? • The focus on deaths and serious injuries • Using F&S crashes or estimating DSIs using severity ratios • Identifying high risk intersections. • Using injury crash data and estimating DSIs from typical severities. No risk assessment tools equivalent to KAT • Crash types that result in deaths and serious injuries • More focus on severe crash types e.g. side impacts, pedestrians and cyclists. • Considering how countermeasures affect crash severity • Roundabouts, barriers and clear zones • Crash prediction models and crash severity / casualties • Still requires development – using typical severities.

  27. Developing the forward SH programme • Strategic assessment – SafetyNET – now includes intersections • Safety works prioritised on DSIs saved / project life / $100m

  28. Red Light Running – about one third • Failed to notice red signal • Brightness • Location, location, location • Background distraction / confusion • Progression expectation • Inconsistent phasing - arrows

  29. Right turn against (LB) – nearly one third • geometric - visibility • judging speed, intentions - multilane • turning on yellow - one lane stops • through or turning left? • phasing & arrows

  30. Right turn arrows • Reduction in LB crashes due to arrows: (Hall TRRL) • filter then lag right turn arrow: 30% • lead right turn arrow then filter: 68% • lead right turn arrow (no filter): 90% • Problem with lag turns – amber trap

  31. Countermeasures – What have we learnt? • Turn lanes mixed blessing • Right turn lanes - reduce low severity rear ends but if not aligned well (typical), are visibility block – increase risk. Also more lanes speed up through vehicles into turning traffic. • So may increase high severity crashes while reduce low severity type. • While shared left / through lanes not as bad since GW rule changes – (indicating left but travel through) but still much worse for cyclists. • Right turn against – mostly a multilane issue.

  32. Pedestrian Conflicts - crossroads • One fifth to one quarter – higher in CBD • Injury F&S • Ped Crossing from left 136 36 • · Ped crossing from right 77 16 • · Car turns left ped from left 42 11pedfrom right 19 3 • · Car turns right ped from left 115 24pedfrom right. 77 15

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