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Home > Forums > Civil / Environmental Engineers > Activities > Civil/Environmental engineering other topics Forum

Minimum transition length to merge from three lanes to two lanes dual carriageway(2)

Read More Threads Like This One

SHOOTZ (Civil/Environmental)

9 Jul 12 9:26

Am designing a three lane dual carriage road (two lanes for private cars one lane for Buses only on each side). At a certain point along the road where the traffic is low we are merging the three lanes to two lanes. What is the recommended transition length required to merge? I will also appreciate if I get a reference standard. The design speed is 60km/hr and lane width is 3.5m.
Thanks

dicksewerrat (Civil/Environmental)

9 Jul 12 11:55

Since you are not in US, DOT spevcs wouldn't apply. Call your local Road Authority.

Richard A. Cornelius, P.E.
WWW.amlinereast.com

SHOOTZ (Civil/Environmental)

9 Jul 12 16:37

yes am not in US but we are allowed to use US or BS metric standards, brt system is very new to our country most of the specs we borough from aashto and uk standards.

gbam (Civil/Environmental)

9 Jul 12 18:26

Design Speed to one in USA, if I remember correctly. For 60 mph and 12-ft lane drop --> 720-ft. Dot exactly sure how that would translate to metric, however. Quick translation to US units and back to metric results in 135 m +/-.

Hoaokapohaku (Geotechnical)

9 Jul 12 22:01

In the USA, for speeds 70 km/hr (45 mph) or more, gbam's memory is correct. For lower speeds, the correct distance is the square of the formula provided by gbam, divided by 60.

The standard, with formulas, detailed explanation and drawings can be found at http://mutcd.fhwa.dot.gov/htm/2003r1/part3/fig3b-1....

Debaser (Civil/Environmental)

10 Jul 12 6:56

In Chapter 5 of the Traffic Signs Manual (UK), Figure 4.13 shows the standard practice for reducing the number of lanes from 3 to 2.
http://assets.dft.gov.uk/publications/traffic-sign...

Refer also to Volume 6, Section 1 'Links', of the DMRB.
http://www.dft.gov.uk/ha/standards/dmrb/vol6/secti...

Debaser (Civil/Environmental)

10 Jul 12 7:04

Further to my previous post, 'Table 4.3: Mainline Change in Width Based on a Standard 3.65m Lane' of TD27/05 'Highway Cross Sections' gives various tapers based on design speeds. For a 60kph design speed the taper should be 1:30.

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