Ecg554 Topic 3i

TRAFFIC IMPACT ASSESSMENT (ECG554) TOPIC 3.0: FUNDAMENTAL OF TRAFFIC ENGG. APPLICATION FOR TRAFFIC IMPACT ASSESSMENT (TIA) Synopsis: This topic covers: Fundamental of traffic stream characteristics and scope under level of service evaluation. Learning Outcomes: At the end of the topic students should be able to; 6. Describe the characteristics of traffic stream under various travel conditions,, 7. Evaluate basic capacity of roadway under ideal condition, and 8. Assess the level of service of facilities.

Traffic Engineering • Recapitulate ECG 504: – Traffic engineering: deals with the safe and efficient movement of people and goods on roadway. It includes; planning, geometric design, traffic operation and control, traffic safety, maintenance and management of traffic. – Elements of traffic engineering: • • • •

Studies and data collection, Geometric design, Capacity analysis and evaluation, Control, operation and management

– Work of traffic engineer: quantifying how well a facility or system working, for the purpose of, • • • •

Assessing existing condition, Evaluating alternative improvements, Quantifying associated costs and benefits, Communicating the results to both technical and non-technical audiances

Traffic Stream Characteristics

Volume Characteristics • Traffic volume are distributed in both time and space

Volume Characteristics: Hourly variation in traffic volume

Volume Characteristics: Daily variation in traffic volume

Volume Characteristics: Seasonal variation in traffic volume

Speed Characteristics: Speed distribution • Each vehicle in a traffic stream has a different speed. Most traffic streams have speeds that are normally distributed which is consistent with driver behavior.

Speed Characteristics: Presentation of speed distribution • Frequency distribution curve • Cumulative frequency distribution curve

Basic Capacities under Ideal Conditions (Textbook page: ) • Traffic volume • Capacity – Ideal capacity – Practical capacity

Capacity for Uninterrupted Flow Facilities • Under ideal conditions, possible capacity for uninterrupted flow are: – For 2-lane two way (total) = 2,000 pcu/h – For multilane (per lane) = 2,000 pcu/h

• Ideal conditions for two-lane roads are: – – – – – – – –

Design speed equal or greater than 100 km/h, Lane width equal or greater than 3.65 m, Clear shoulder wider than or equal to 1.83 m, No “No passing zone” on the highway, All passenger cars in the traffic stream, A 50/50 directional split of traffic, No impedance to through traffic due to traffic control or turning vehicle, Level terrain

Capacity for Interrupted Flow Facilities • Capacity of signalized intersection approaches – the saturation flow rate is used. Saturation flow rate of an intersection approach lane is the amount of traffic volume that can be discharge during the green time and that can be sustained constant. • Saturation flow rate for signalized approaches is 1800 pcphgpl under ideal conditions, which include: – – – – – –

Lane width of 3.5 m, Level approach grade, All passenger cars in the traffic stream, No left- or right turning vehicles in the traffic stream, Intersection located in a non-CBD area, No parking within 76.2 m (250 ft) from intersection

Level of Service Concept (LOS) • • •

LOS is defined as qualitative measure describing operational conditions within a traffic stream and their perception by motorists. Facilities performance measured in term of LOS index, and is letter coded from A (excellent quality of flow) – F (unsatisfactory operation) Parameters used are: – Volumes or flow rates • Demand volume • Discharge volume

– Speeds or delay • Average travel speed/spot speed/space mean speed • Delay per vehicle (seconds)/stopped delay/total delay

– Trip times • Average travel time

– Demand to capacity ratio • V/c ratio