Ryan Sager Chapters 9 and 10

Traffic Engineering Studies

Volume Studies and Characteristics

Volume Detection

Methods of Detection

Volume Characteristics

Counts and Adjustments

Manual Counts – manual counts are still done because for short counts they are economical, and mechanical and electronic counters are not always accurate – due to human error, count adjustment factors are needed [1]

Intersection Volume Studies

Volume Studies and Characteristics

Adjustments

Intersection Volume Studies

Purpose of Studies

Presentation of data can be done a number of ways

- Tables can help breakdown vehicle classifications

- Elaborate graphics are usually used for peak-hour and/or full-day volumes

Miles Traveled

Some methods may require adjustments to counts, such as counting axles on vehicles to determine % of heavy vehicles

Source: http://www.iowaltap.iastate.edu/documents/TN/2004/sep-oct/spot_speed.htm

Arrival versus Departure Volumes – usually

discharging volume is counted at intersections,

but when demand is greater than capacity, queue

is formed and discharge volume is never greater

than capacity [1]

Therefore, adjustments must be made to discharge

counts to estimate demand

Manage the road system, investigate trends over time, understand the needs of the public and industry, and assess

the effectiveness of improvements [1]

Types of studies: volume studies, speed studies, delay studies, accident studies, parking studies, transit studies, pedestrian studies [1]

Volume – the number of vehicles passing

a point during a specified time period,

which is usually one hour [1]

Rate of Flow – the rate at which vehicles

pass a point during a specified time period

less than one hour, expressed as an

equivalent hourly rate [1]

Estimating Vehicles Miles Traveled on a Network

Portable Count Techniques

Accumulate a total count for the period of the study [1]

[1]

Source: http://www.mdt.mt.gov/publications/datastats/traffic_factors.shtml

Source: www.sciencedirect.com

Output of most limited-network volume studies is an estimate of the total vehicle-miles traveled (VMT) [1]

Estimate is done roughly by assuming that a vehicle counted on a link travels the entire length of the link [1]

Types of Counts

Limited Network Volume Studies

Study Times

Field Techniques for Volume Studies

Control Counts – taken at selected representative locations to measure and quantify demand variation patterns in time. These are maintained continuously throughout the study period [1]

Small-network volume studies are intended to determine the amount and pattern of traffic flow over a limited network of street links and intersections during a specified time interval [1]

Source: http://www.iowaltap.iastate.edu/documents/TN/2004/sep-oct/spot_speed.htm

Volume counts, vehicle occupancy,

turning movements at intersections,

vehicle classifications [1]

Source: www.maps.google.com

One day study (8-hour) – needs two crews, one at the control station (8-hours) and the other at coverage count stations (1-hour each) [1]

Multi-day Study (6-days) – needs two crews, one at the control count station (8-hours everyday) and the other at coverage count stations (8-hours each) [1]

Multi-day Study (3-days) – needs two crews, one at the control count station (8-hours everyday), and the other at coverage stations (4-hours each) [1]

[1]

Coverage Counts – Coverage counts are taken at all locations for which data is needed. They are conducted as samples, with each location being counted for only a portion of the study period [1]

Source: www.fhwa.dot.gov

Demand – the number of vehicles that desire to travel past a point during a specified period, usually on hour [1]

Permanent Count Techniques

[1]

Capacity – the maximum number that can be expected to be served in the given time period [1]

When capacity constraints exist upstream, demand cannot be measured downstream,

because the discharge volume is NOT demand but bottleneck capacity volume. [1]

Source: www.maps.google.com

Source: http://www.iowaltap.iastate.edu/documents/TN/2004/sep-oct/spot_speed.htm

Large Scale Counting Programs

Statewide Programs

Statewide Counting Programs

Locations can be either Permanent Counts or Major or Minor Control Counts [1]

They must calibrate daily variation patterns and monthly or seasonal variation patterns for the full 365-day year [1]

There are methods for calibrating daily, monthly, and seasonal factors [1]

Other Counts

Objectives:

Conduct coverage counts every year on every 2-mile segment of the state highway system except for low-volume roads (AADT<100 veh/day) [1]

Produce an annual estimate of AADT for each coverage location [1]

One control-count location is generally established for every 20-50 coverage count locations, depending on characteristics of the region [1]

Cordon Counts – when vehicle accumulation

within an area is needed. Used when you want to establish a CBD or other major activity center where accumulation of vehicles is of important interest. [1]

[1]

Source: www.images.google.com

In conclusion, counts should

be established in some form

of this order:

Specialized Counting Studies

Screen Line Counts – when changes in traffic flow from one area to another is needed. Typically use home interviews as the primary methodology. [1]

Specialized Counts

Specialized OD Studies

If you have many transponders used for Toll Roads, you can automatically collect OD through License Plate studies

Origin and destination Counts – used for regional planning and traffic applications [1]

For regional applications, massive home interviews are needed, while for traffic applications, the counts are more limited to weaving-area studies, freeway studies, or major activity center studies [1]

Conventional traffic origin and destination counts rely on one of three approaches:

License plate Studies

Postcard Studies

Interview Studies

Source: www.fhwa.dot.gov

Source: http://www.iowaltap.iastate.edu/documents/TN/2004/sep-oct/spot_speed.htm

Source: www.images.google.com

Source: http://www.iowaltap.iastate.edu/documents/TN/2004/sep-oct/spot_speed.htm

Speed, Travel Time, and Delay Studies

Travel Time

Measurement Techniques

Speed, Travel Time, and Delay Studies

Travel Time Studies

Spot Speed Studies

Document the distribution of vehicle speeds as they pass a point or short segment on the roadway [1]

Data is used to establish the effectiveness of speed limits, determine speed trends at local, state and national level [1]

Methods of Measuring

Floating Car Technique – test-car driver is asked to pass as many vehicles as pass the test car, so that the cars position remains unchanged in the traffic stream [1]

Maximum Car – driver is asked to drive as fast as is safely practical in the traffic stream [1]

Average Car – driver is asked to drive at the approximate average speed of the traffic stream [1]

Source: www.ops.fhwa.dot.gov

[1]

Source: http://www.iowaltap.iastate.edu/documents/TN/2004/sep-oct/spot_speed.htm

[1]

Source:http://ops.fhwa.dot.gov/trafficanalysistools/tat_vol4/sec2.htm

[1]

Source: www.youtube.com

[1]

Delay Studies

Collecting Data for Studies

Which Delay?

New Methods!

Collecting Data

When are you fully “stopped”

Differences between Running Time and

Stopped Delay Time – fully stopped

Stopped Delay - the time a vehicle is stopped in queue while waiting to pass through an intersection

Approach Delay - includes stopped delay but adds the time loss due to deceleration from the approach speed to a stop and time loss due to reacceleration back to the desired speed

Time-in-Queue Delay - total time from a vehicle joining an intersection queue to its discharge across the STOP line on departure

Total Control Delay - time-in-queue delay plus time losses due to deceleration from and acceleration to ambient speed

Cell Phone Methods

[1]

Source: http://www.fhwa.dot.gov/ohim/tvtw/natmec/00020.pdf

Cell phone methods can also be used today, collecting GPS data to monitor their positions and how many are projecting positions on a roadway at any given time

Source: http://www.fhwa.dot.gov/ohim/tvtw/natmec/00020.pdf

How do you observe?

Intersection Delay Studies

Source: - http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0049171

Based on direct observation of vehicles-in-queue at frequent intervals and requires a minimum of two-observers.

The first observer keeps track of the end of standing queues for each cycle by observing the last vehicle in line. Regular interval observations will be taken to record the vehicles in queue at those times. The second observer keeps count of vehicles arriving during the survey period and stop. Stopped vehicles are only counted once, regardless of how many times they are counted.

[1]

Source: http://www.briggsdodge.com/blog/wp-content/uploads/2013/05/9848648-car-speedometer-for-racing-design.jpg

Source: www.images.google.com

Source: http://www.sciencedirect.com/science/article/pii/S0191261503000031