Norman W. Garrick Travel Flow Data Some Basic Concepts Good travel flow data for all modes of travel is important for transportation planning and design.

Norman W. Garrick

Travel Flow Data Some Basic Concepts

Good travel flow data for all modes of travel is important for transportation planning and design. For example, vehicle traffic flow is one of the data sets used to estimate carbon emissions from transportation activities.

One of the challenges is that travel flow varies significantly in both space and time. We often do not have data at a fine enough resolution to fully capture these variations. It is important to understand the likely variations in order to effectively interpreter the available data

Norman W. Garrick

Temporal Variation in Traffic Flow

Traffic flow vary by time of day, day of week, month of year and from year to year.

The pattern of variation depends on the specific location. For example, the temporal variation of traffic in Storrs is very different from that in Willimantic.

Monday to ThursdaySaturday

http://www.ptt.uni-duisburg.de/en/projekte/babnrw/daten/

Norman W. Garrick

Temporal Variation in Traffic Flow

One solution that is some times used to reduce temporal variation is differential pricing.

For example, many transit systems charge a higher rate for travel before 10 am and after 3 pm. This helps encourage people that have flexible plans to delay their travel to the off peak time.

This is the same approach used on some toll roads where the plan is know as congestion pricing.

Norman W. Garrick

Spatial Variation in Traffic Flow

http://www.interstate-guide.com/images/i-077_va_aadt.gif

Norman W. Garrick

Spatial Variation in Traffic FlowDirectional Variation

Reversible lanes in the middle to deal with a severe directional variation.

(I believe this is just conceptual – I don’t know of any example of reversible lanes implemented in this manner.

Norman W. Garrick

Directional Distribution

In many urban areas trips are mostly going towards the central business district in the morning and from the CBD in the evening. This means that the trains and the roads are sized to carry the peak direction flow. If the directional distribution is very lopsided then this is a very inefficient system since the lanes and the trains going away from the center will be virtually empty in the morning.

One argument for mixed land use is that it helps to cut down on this directional over balance. So if a train is connect two mixed use centers (such as downtown DC and Arlington, Virginia) the directional distribution will be more balanced resulting in more efficient use of the transportation system.

Norman W. Garrick

Where does travel flow counts come from?

State Counts of Vehicle Traffic

The DOT maintain a program for counting traffic on all state owned highways, roads and streets.

There are two different type of counts: permanent count stations and temporary count stations

Permanent Count Stations give the most complete coverage of temporal variation in traffic

Temporary count stations are much less reliable since they are put out for at most 48 hours – the state then use factors to estimate the average daily count.

Other source of traffic count data are counts from individual towns or from developers working on larger projects.

Norman W. Garrick

Where does travel flow counts come from?

Pedestrian, Bikes and Transit Counts

I know of no agencies that routinely count pedestrian traffic – this makes it harder to include pedestrian issues in transportation planning

A handful of cities in the country, including Portland, Davis and Cambridge have programs for counting bike traffic

Transit counts are readily available from transit agencies and national transit bodies

Bikeway MilesCyclists per Day

1991 2007

Portland (OR) Bike Count Program

http://www.streetsblog.org/wp-content/uploads/2007/09/portland_bike_counts.jpg

Norman W. Garrick

Biking, Davis (CA)

Norman W. Garrick

Shared Bikes, Paris

Norman W. Garrick

Bike Parking at Train Station, Amsterdam

Norman W. Garrick

Light Rail, Portland (OR)

Norman W. Garrick

What is the State Traffic Counts Used for?AADT

The state traffic count is used to estimate an average annual daily traffic (AADT)

The AADT is meant to represent the average traffic over all 365 days in the year. In other words, it is meant to be

Total Traffic in year / 365

This can be obtained relatively accurately from the permanent count stations.

From the temporary stations, this is more difficult. The count from the station (which is referred to as average daily traffic or ADT) is multiplied by seasonal and day of the week adjustment factor to get an estimated AADT.

Norman W. Garrick

Characterizing Traffic Counts

Vehicles/hr or AADT

Often reports from state level traffic count studies give average annual daily traffic (AADT)

Since hourly volume for the design hour is what is typically used for design it is left up to the designer to come up with a reasonable design hourly volume from the AADT

As a very rough guide the typical design hour volume is can be taken as about 10% of the AADT. But this % varies significantly depending on the temporal variation in traffic.