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Auxiliary Lanes in Rural Road

Auxiliary Lanes in Rural Road

Auxiliary Lanes in Rural Road

I'm currently working on a project where the access road to a small residential development connects to an existing two-lane two-way road at right angle.

The existing road has a posted speed of 80 kph. The access road is a dual carriageway with a posted speed of 40 kph. The roads and the project site are situated in a rural area where there are no adjacent developments and where traffic volumes are low. I only have initial traffic information entering the site---about 5-10 buses and 500 cars a day.

I have initially designed the connection as a simple junction. However, I was told that auxiliary lanes are required (acceleration/deceleration lanes) due to the posted speed of the existing road. But traffic volumes should also be taken into account, correct?

I don't have much experience on this and any advise/inputs will be greatly appreciated. What do you think? I am concerned that providing auxiliary lanes for this situation might be an overkill and would pose higher construction costs for the Client.

Thanks in advance.

RE: Auxiliary Lanes in Rural Road

How many vehicels are using the main road? If your site traffic is about 500 vpd, I'm not surprised they are asking for turn lanes.

One US study found that left turn lanes on rural roads have been shown to cut the crash rate nearly in half. I'm not sure this is considered in many volume warrants for left turn lanes.

It would help if you said which country you're in. I could point you towards U.S. documents, but they may not help you. Since you're using metric units, I figure you must be from some place less backwards than the US, Myanmar or Liberia.

     Maybe the tyranny of Murphy is the penalty for hubris.  - http://xkcd.com/319/

RE: Auxiliary Lanes in Rural Road

Thank you, ACtrafficengr. The project site is in the UAE.

I do not have the traffic volumes on the main road for now, I was told that the traffic impact study will be completed in a month or so.

By the way, the auxiliary lanes are only being provided at one side of the road (entry to and exit from the site). Providing a left-turn lane along the existing road due has not been considered.

If you could point me to the U.S. documents you were referring to, it would be a big help. We do use AASHTO from time to time as secondary reference. :)

RE: Auxiliary Lanes in Rural Road

Going by TD42/95 of the DMRB (http://www.dft.gov.uk/ha/standards/dmrb/vol6/section2/td4295.pdf) then providing deceleration/acceleration tapers would seem over the top given the information provided. The closest parameter which would require these tapers to be provided would be the speed of traffic on the main road. In our case that would be 85kph, although there is scope to provide them when speeds are lower (see para. 7.49 of the TD, onwards).

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