Lecture #12 Arterial Design and LOS Analysis

Objectives  Understand the factors in arterial design Understand how arterial LOS is determined

Kramer’s Ten Ideal Arterial Characteristics Arterial split of 2/3 to ¾ at all intersections Progressive movement in both directions Protected left turns used to protect through traffic Left turn bays provided, with protected phase Accommodates large trucks Protected pedestrian phases and frequent crossings Transit operations that does not impede through traffic Transit stops at locations close to protected pedestrian crossings Accommodate future growth with minimal effect on through traffic Variable timing and progression to accommodate variable traffic, special events, and emergency vehicles

Arterial Performance Average travel speed of through vehicles  length = arterial or segment length (miles)  running time per mile = total of running time per mile on all segments in the arterial or section (sec)  total intersection approach delay = totaled over all intersections within the arterial or section (sec)

Signal Spacing How can the arterial function be preserved? Why is signal spacing is crucial? How might signal coordination be better than physical improvements? What tends to happen to arterial LOS as signalized intersections increase?

Advanced Planning What needs to be considered when planning an arterial? What are the general planning alternatives?

Reallocation of Arterial Space Parking How can arterial space be reallocated?

Other Aspects of Operation What is the overall effect of intersection modifications? – Turn bays (left and right) Existence Length – RTOR – Turn prohibitions – Arrival patterns – Signalization

Other Aspects of Operation (cont.) What is the overall effect of arterial modifications? – Signal spacing – Parking – Transit – Delivery activity – Land access function – Special use lanes

HCM Procedure for Arterials What are the steps to the HCM procedure? Establish arterial to be considered Determine arterial class and free flow speed Define arterial sections Compute running time Compute intersection approach delay Compute average travel speed –Section –Facility Assess the LOS

HCM Procedure for Arterials (cont.) What does the procedure do? Why are there different arterial classes? How are the arterial classes identified?

Arterial Speeds Free flow speed How can running speed be determined? How can intersection delay be determined? Average travel speed What is the correct delay to use in arterial evaluation? – D = 1.3d Where D = approach delay (sec/veh) d = stopped delay for the through movement (sec/veh)

Arterial vs Intersection Performance How are arterial and intersection performance related? Good arterial performance requires great intersection performance How can good arterial performance be assured?