Chapter 1 Traffic Flow What you will be learning from this chapter … TRAFFIC STUDIES Traffic Volume Spot Speed TRAFFIC FLOW THEORY Traffic Flow Parameters Speed, Flow & Density Relationship CAPACITY & LEVEL OF SERVICE Multilane Highway Capacity Study

TRAFFIC STUDIES May grouped into Inventories – existing information that related to street width, parking space, transit routes, traffic regulation etc. Administrative studies – existing engineering record. Eg. Result of survey (field measurements) Dynamic studies – study on current operational condition. Eg. Speed, traffic volume, travel time etc.

TRAFFIC VOLUME STUDY Traffic volume is ...... the number of vehicles passing a given point during a specified period of time. (The time is varies from as little as 15 minutes) Data collected may be put into subclasses such as: Directional movement Occupancy rates Vehicle classification Pedestrian age Traffic volume studies are usually conducted when certain volume characteristics are needed such as: Average Annual daily Traffic (AADT) – average of 24-hr counts collected everyday of the year. It used for Estimation of highway user revenues Computation of crash rates in terms of number of crashes per 100 million vehicle miles

Average Annual daily Traffic (AADT) – average of 24-hr counts collected everyday of the year. It used for Estimation of highway user revenues Computation of crash rates in terms of number of crashes per 100 million vehicle miles Establishment of traffic volume trends Evaluate the economic feasibility of highway projects Develop freeway & major arterial street systems Develop improvement & maintenance programs Average Daily Traffic (ADT) – average 24-hr counts collected over a number of days greater than one but less than a year. It used for: Plan highway activities Measure current demand Evaluate existing flow Peak Hour Volume (PHV) - maximum number of vehicles that pass a point on a highway during a period of 60 consecutive minutes . Used for: Functional classification highway Design geometric of highway (lane, lane width, shoulder etc) Capacity analysis Parking regulation

Vehicle classification (VC) – records volume based on type of vehicle Vehicle classification (VC) – records volume based on type of vehicle. Eg. car, motorcycle, truck etc. It used for Design the road geometric with particular reference to turning-radii, max. grades, lane widths etc. Capacity analysis with respect to passenger-car-equivalents of trucks Adjust traffic count obtained by mechine Structural design of highway pavements, bridge etc. Classification counts should be conducted if: the percentage of heavy trucks is high vehicle mix at crash site is acontributing factor to the crash problem Vehicle Miles of Travel (VMT) – measure of travel along a section of road

The importance of traffic volume study ...... For traffic planning, design & research. To determine the efficiency of a traffic system. To evaluate the quality of service of a transport facility. To design roads – number of lanes & pavement thickness. Volume study methods ...... Manual Count Methods Automatic Count Methods

METHOD OF CONDUCTING VOLUME COUNTS 2 Basic method: Manual method involve 2 – 3 persons recording the number of vehicles using counter applicable for vehicle volume studies at intersection Automatic method uses an automatic counter those that require surface/subsurface laying counter detector. eg. pneumatic road tubes or magnatic counter those do not require laying detector

Counting periods The time and length that a specific location should be counted is also dependent upon the data desired and the application in which the data are to be used 24-hour counts (24-hour period between noon Monday and noon Friday). 16-hour counts from 6 a.m. to 10 p.m. This period contains most of the daily flow including evening traffic. 12-hour counts (from 7 a.m. to 7 p.m. to cover most daytime traffic movements, especially in commercial or business areas. Such counts made in shopping centers or districts where stores are open at night are usually extended until after 9 p.m). Peak-period counts which vary depending upon size of metropolitan area, proximity to major generators (such as the CBD or industrial areas), and the type of the facility (gateway, radial arterial, etc.). Commonly used periods are 7 to 9 am and 4 to 6 p.m.

Counting periods Special conditions should be avoided unless the purpose of the count is to obtain data concerning these unusual conditions. Examples of such conditions include: Special events (holidays, sports, exhibitions, sales., etc). Abnormal weather conditions which do not generally occur. Temporary closure of streets effecting the volume pattern. Transit or trucking strikes.

MANUAL COUNT Manual Count method ...... BFC3082 Traffic and Road Safety Engineering Lecturer: Mr. Basil David Daniel MANUAL COUNT Manual Count method ...... Applied when small sample of data is required. For periods less than one (1) day. Normal intervals are 5, 10 or 15 minutes. Counts are not usually taken on Mondays, Fridays and weekends. Can anyone explain why ? Manual Count recording methods ...... Tally Sheets Mechanical Counting Boards Electronic Counting Boards

MANUAL COUNT Manual counting board Tally sheet Electronic counting board

AUTOMATIC COUNT Automatic Count method ...... Applied when large sample of data is required. For periods more than one (1) day. Normal intervals are 1 hour for a 24 hour period. Counts may extend to a week, month or year. Automatic Count recording methods ...... Portable Counters Permanent Counters Videotape

AUTOMATIC COUNT PORTABLE COUNTERS Traxmite Pneumatic Road Tube & Recorder Hi-Star Portable Traffic Counter PERMANENT COUNTERS Loop Detector

SPOT SPEED STUDY

What is a Spot Speed Study? Spot speed studies are used to determine the speed characteristics of a traffic stream at a specific location along the roadway.

Why Spot Speed Studies? Determine existing roadway speeds Evaluate effectiveness of speed enforcement programs Identify the speed impact of roadway geometry and roadway features Determine impact on speed of traffic control devices Provide evidence to support/refute excessive speed complaints

SPOT SPEED STUDY Spot speed study ...... A study of speed of traffic at one point or spot on a trafficway. Consists of a series or sample of observations of individual speeds of vehicles approaching an intersection or passing a point at a non-intersection. Used to estimate the speed distribution of an entire traffic stream at that location under prevailing traffic conditions. Spot speed studies are carried out at ...... Trend locations – straight, level, open sections of rural highways, and midblock at urban streets. Problem locations – accident blackspots, and locations where traffic signals and signs are contemplated. Representative locations – for basic data surveys. Locations of before-and-after studies.

Spot Speed Study Steps STEP 1 --- Organize Study Plan STEP 2 --- Select Data Collection Technology STEP 3 --- Select Appropriate Site and Collect Field Data STEP 4 --- Reduce and Analyze Data STEP 5 --- Interpret and Report Findings

STEP 1. Organize Study Plan Reason for Study Identify Problem Plan Logistics Select Date and Time Select Location Number of Vehicles to Observe

Time and Date Selection Recommended - Reflect normal driving conditions Late spring or early autumn Tuesday, Wednesday or Thursday Not Recommended: Unique events Inclement weather Holidays Peak travel times

Location Selection - Reflect normal driving Recommended: Free flow conditions Uniform roadway segments Not Recommended: Traffic signals and other junctions Intersections Curves Work zones Parking zones Active crosswalks

STEP 2. Select Data Technology

STEP 2. Select Data Technology

Handheld Technologies Handheld radar or LiDARmeters to identify vehicle speeds Speeds are recorded manually on a data sheet Minimum data requirements must be met to ensure quality of data Efforts must be made to reduce bias

In-Road Technologies Disruption of traffic flow during installation and maintenance Safety concerns for operating in the road Maintenance issues: Snow removal, street sweepers, flood etc. Heavy vehicle traffic Typically well established technologies

Out-of-Road Technologies

STEP 3. Collect Field Data

STEP 3. Collect Field Data

Additional Safety Considerations

STEP 3. Collect Field Data

STEP 4. Reduce and Analyze Data

SPOT SPEED STUDY STOPWATCH METHOD

SPOT SPEED STUDY RADAR METER METHOD

SPOT SPEED STUDY PNEUMATIC ROAD TUBE METHOD Recorder Pneumatic Road Tubes

ANALYSIS OF SPOT SPEED DATA Spot speed data can be presented as: frequency distribution table. frequency and cumulative frequency distribution curve common descriptive statistics The mean speed The median speed The pace the standard deviation the 85th and 15th percentile speeds