Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

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

Status
Not open for further replies.

SHOOTZ

Civil/Environmental
Joined
Nov 11, 2011
Messages
12
Location
TZ
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
 
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.
 
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 +/-.
 
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
 
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.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top