Slip lane

This article relates to at-grade intersections. For the British term referring to acceleration lanes at a grade-separated junction, see Interchange (road).

In road design, a slip lane is a road at a junction that allows road users to change roads without actually entering an intersection.[1] Slip lanes are "helpful... for intersections designed for large buses or trucks to physically make a turn in the space allotted, or where the right turn is sharper than a 90 degree turn."[2] Slip lanes may reduce congestion and "t-bone" motor vehicle collisions, but they increase the risk for pedestrians, cyclists and horse riders who cross the slip lane.

Illustration (left-hand traffic): the blue vehicle in the slip lane must normally give way to the green and red vehicles once they are on the major road.

Some intersections that are controlled by traffic light offer a slip lane, which allows users to bypass the lights when they turn. That helps ease congestion and improves journey times, as people who are turning do not have to stop at the light but can continue at the same speed.[3] There are two types of slip lanes at intersections: slip lanes that end and require traffic to merge to join the main road, and slip roads that continue onto the main road as another traffic lane.

Terminology

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They are known as "filter lanes" in the United Kingdom. In right-turn countries, they may be called "channelized right-hand turn lanes."

Rules

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In Australia, before entering a slip road, drivers must look to ensure that their blind spots are clear of other motorists, cyclists, and pedestrians. Drivers must then give way to any pedestrians crossing the slip road. Before joining the main road from a slip road, drivers must give way to all other traffic even if they are faced with a give-way or with other traffic controls.[4]

Pedestrians

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A right-turn slip lane in the United States (center of photo), including a pedestrian crossing.

In countries such as the United Kingdom in which partial conflicts between pedestrians and vehicular traffic are not permitted, slip lanes can be used as part of a "walk with traffic" facility. Normally, pedestrian signals in the UK operate on a full pedestrian stage in which all traffic is held at red, and all pedestrian crossings are given a green signal. With a slip lane, pedestrians can cross to the triangular island during the vehicle red phase and cross the road while the traffic from their approach has a green light.[5]

The Federal Highway Administration (FHWA) in United States has indicated that "to accommodate safe pedestrian crossings," intersections should be designed "using tight curb radii, shorter crossing distances, and other tools.... While right-turn slip lanes are generally a negative facility from the pedestrian perspective due to the emphasis on easy and fast vehicle travel, they can be designed to be less problematic."[6]

In right-turn countries, designers of right-turn slip lanes may try to increase pedestrian safety by including a range of features. These may include "a raised "island" for pedestrians with a curb and ramps for wheelchair users. To encourage drivers to slow down for crossing pedestrians, edge lines or painted cross-hatching may be used to "narrow the [driver's] perceived width of the lane."[7] As well, pedestrian safety in the crosswalk may be improved with "high-visibility crosswalk striping, flashing beacons, and/or signage" and raised crosswalks. Flashing "warning beacons may be desirable in locations where there are high traffic volumes and vehicle speeds."[8] Some states in the United States require a stop sign at slip lanes to control entry to the main roadway.[9]

The organisation Strong Towns argues that slip lanes exist only to prioritise the speed of motor traffic, and it calls for the removal of slip lanes on local streets.[10]

When poorly designed, slip lanes can be a dangerous design element. For reasons of urban design and pedestrian safety, many road-controlling authorities are actively removing them in urban and suburban settings.[11][12] Slip lanes may need to be removed if considerations such as pedestrian safety grow to a point that they override the desire to facilitate free passage for drivers.[13][14] "Slip lanes reduce drivers’ awareness of crossing pedestrians because they are led to focus on the traffic stream into which they are merging, and also impair visibility of the traffic stream because of the angle of approach."[15] As well, "[s]lip lanes also greatly increase crossing complexity for pedestrians and cyclists, by increasing total crossing distance, requiring judgement about crossing fast-moving traffic without the benefit of a traffic signal."[16] To minimise risks of collision, slip lanes can be shaped to enter the traffic flow at an angle higher than the 45 degrees that is shown in the sketch. Such lanes are called high-entry angle slip lanes.[17]

Further reading

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  • Fitzpatrick, K., Schneider IV, W. H., & Park, E. S.(2006). Operation and Safety of Right-Turn Lane Designs. Transportation Research Record, 1961, 55–64.
  • Naik, B., Appiah, J., Khattak, A. J., & Rilett, L. R. (2009). Safety Effectiveness of Offsetting Opposing Left-Turn Lanes: A Case Study. Journal of the Transportation Research Forum, 48(2), 71–82.
  • O'Brien, M., O'Brien, A., Liu, J., Michaux, G., & Nahlawi, H. (2012). Pedestrian Safety at Slip Lanes and Alternative Turn Lane Treatments. Transportation Research Record, 2299, 110–120.
  • Persaud, B., Lyon, C., Gross, F., & Eccles, K. (2010). Safety Evaluation of Osset Improvements for Left-Turn Lanes. Transportation Research Record, 2171, 44–51.
  • Potts, I. B., Bauer, K. M., Torbic, D. J., & Ringert, J. F. (2013). Safety of Channelized Right-Turn Lanes for Motor Vehicles and Pedestrians. Transportation Research Record, 2398, 93–100.
  • Schnell, T., Neyens, D. M., Lee, Y.-C., & Aktan, F. (2004). How to More Safely Accommodate Pedestrians Through an Intersection with Free-Flow Legs. St. Paul, MN: Minnesota Department of Transportation Research Services Section.
  • Tarawneh, M. S., & McCoy, P. T. (1996). Effect of Offset Between Opposing Left-Turn Lanes on Driver Performance. Transportation Research Record, 61–72.

See also

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References

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  1. ^ "Pedestrians crossing slip lanes" (PDF). Main Roads Western Australia. September 2002. Retrieved 8 November 2015.
  2. ^ Davis, Stephen Lee (5 November 2019). "Slip Lanes Would Never Exist if We Prioritized Safety over Speed". Strong Towns.
  3. ^ Davis, Stephen Lee (5 November 2019). "Slip Lanes Would Never Exist if We Prioritized Safety over Speed". Strong Towns.
  4. ^ "Road Rule Changes". cota-act.org.au. Archived from the original on 8 February 2008.
  5. ^ "Chapter 6, Traffic control". Traffic signs manual. London: Department for Transport, Northern Ireland. Department for Infrastructure, Scotland. Scottish Government, Wales. Welsh Government. 2019. ISBN 978-0-11-553744-8. OCLC 1134444798.
  6. ^ Davis, Stephen Lee (5 November 2019). "Slip Lanes Would Never Exist if We Prioritized Safety over Speed". Strong Towns.
  7. ^ "Pedestrian Safety Guide and Countermeasure Selection System". www.pedbikesafe.org. Federal Highway Administration. Retrieved 6 March 2024.
  8. ^ "Pedestrian Safety Guide and Countermeasure Selection System". www.pedbikesafe.org. Federal Highway Administration. Retrieved 6 March 2024.
  9. ^ "Pedestrian Safety Guide and Countermeasure Selection System". www.pedbikesafe.org. Federal Highway Administration. Retrieved 6 March 2024.
  10. ^ "Slip Lanes Would Never Exist if We Prioritized Safety Over Speed". Strong Towns. 5 November 2019. Retrieved 5 January 2022.
  11. ^ "Well Designed Right–Turn Slip Lanes". Federal Highway Administration.
  12. ^ "Cities Are Replacing Dangerous Slip Lanes With Space for People". Streetsblog. July 2018. Retrieved 4 June 2019.
  13. ^ "City Road Draft Master Plan" (PDF). Melbourne City Council. July 2015. Retrieved 8 November 2015.
  14. ^ "Slip Lanes be gone". Matt L. 2 October 2015. Retrieved 8 November 2015.
  15. ^ "B.C. Community ROAD SAFETY TOOLKIT" (PDF). www.nanaimo.ca. City of Nanaimo. Retrieved 7 March 2024.
  16. ^ "B.C. Community ROAD SAFETY TOOLKIT" (PDF). www.nanaimo.ca. City of Nanaimo. Retrieved 7 March 2024.
  17. ^ "Guidelines for the signing and layout of slip lanes" (PDF). NZ Transport Agency. November 1993. Retrieved 9 May 2017.
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