Highway Capacity and Performance Transportation and Highways Engineering

Highway Capacity and Performance Transportation and Highways Engineering Department/Fourth Stage Second Course / Highway Capacity Analysis / Lecture Two

Multilane Highway LOS It is the main road, which connects two or more destinations. This highway has at least more than one lane for the separate use of traffic flow in both the directions. It also has limited access to merging vehicles, has periodical pauses to streamline traffic at signalized intersections with interval not closer than 3. 0 km.

They are normally situated outside urban areas leading to important towns or through rural centers with heavy demand. This will connect primary business centers, from where the travelers make a considerable number of everyday journey. Multilane highways commonly require posted speed limits to be between 40 miles/h and 80 miles/h. They usually have six lanes, with physical medians separating the three lanes of opposite directions of traffic. The same direction traffic lanes will be undivided. The traffic capacity usually varies from 15, 000 to 40, 000 vehicles per day.

A multilane highway contributes to economic development and brings important social benefits. Providing employment opportunities and access to communal, health and education services makes a road network important in fighting against poverty. Free flow speed is an average speed of vehicles on a given segment it is measured under low-volume circumstances. Flow capacity is one of the important parameters in multi lane highway and a quantitative representation of ability to handle traffic. Provided level of service will give a qualitative representation about the condition of traffic situation.

Find Level of Service Intended for analysis of uninterrupted-flow highway segments Signal spacing > 2. 0 miles No on-street parking No significant bus stops No significant pedestrian activities

Chapter 21 of the Highway Capacity Manual For rural and suburban multilane highways https: //sjnavarro. files. wordpress. com/2008/08/highway_capacital_manual. pdf Assumptions (Ideal Conditions, all other conditions reduce capacity): - Only passenger cars No direct access points A divided highway FFS > 60 mph Represents highest level of multilane rural and suburban highways

Lane Width Base Conditions: 12 foot lanes

Lateral Clearance Distance to fixed objects Assumes - More or equal 6 feet from right edge of travel lanes to obstruction - More or equal 6 feet from left edge of travel lane to object in median TLC = LCR + LCL TLC = total lateral clearance in feet LCR = lateral clearance from right edge of travel lane LCL= lateral clearance from left edge of travel lane

- fm: Accounts for friction between opposing directions of traffic in adjacent lanes for undivided - No adjustment for divided, f. M =1

Fa accounts for interruption due to access points along the facility

Estimate Free flow Speed BFFS = free flow speed under ideal conditions = 60 mph FFS = free flow adjusted for actual conditions f. LW, f. LC, f. M, and f. A, for divided multilane highway 10 -foot lane width: f. Lw = 6. 6 mph lateral clearance adjustment for a 4 -lane divided highway with milepost markers located 4 feet to the right of the travel lane. TLC = LCR + LCL = 4 + 6 = 10: f. LC = 0. 4 mph No adjustment for divided, f. M = 1 There are 20 access points per mile: f. A = 5. 0 mph FFS = 60 mph – 6. 6 mph - 0. 4 mph – 0 – 5. 0 mph = 48 mph ( reduction of 12 mph)