Survey Information

Background

Aerial Surveys

The purpose of this ongoing mobility monitoring program is to rate the performance of the Maryland highway system, in order to provide authoritative information to regional planners, stakeholders, and decision-makers. The roots of this program go back to a series of aerial surveys covering traffic flow on Maryland highways in 1976, 1979 and 1984, conducted to assist the Maryland State Highway Administration (SHA) in planning for the large-scale expansion of the network that was done during the 1980’s and 1990’s. The Metropolitan Washington Council of Governments (WashCOG) took note of the SHA aerial survey reports from the earlier years, and in 1993 adopted the methodology to monitor the performance of 330 centerline miles of highway in the Maryland / DC / northern Virginia region (140 of those miles were in Maryland, including the beltway, I-270, and parts of I-95, I-70, US 50 and MD 295). The WashCOG survey was repeated in 1996 and every three years thereafter, allowing analysts to understand how mobility ratings for each link did or did not change between surveys. In 1999 the Maryland State Highway Administration (SHA), the Baltimore Metropolitan Council (BMC), and the Maryland Transportation Authority (MdTA) followed the lead of WashCOG, and initiated a complementary program covering the primary travel routes in the Baltimore metropolitan area; altogether, this new program added approximately 550 centerline miles of Maryland highways to the 140 miles already being covered by WashCOG. Coverage of these two networks was repeated 2002 and 2005.

Information acquired through these surveys gradually became integral to the project review / planning / funding process. Recently, SHA formalized the use of this information in that process, while deciding to expand coverage to include an additional 715 centerline miles of heavily-traveled Maryland highways not otherwise covered. Aerial survey flights of this extended network – now comprising about 1,400 miles in Maryland – were first conducted in the spring of 2008 (the survey area map is available here).

The aerial survey methodology takes advantage of the mobility and vantage point of fixed-wing aircraft, permitting data collection across a large highway network that would not be affordable using traditional ground-based survey methods. During the survey flights, overlapping photographic coverage was obtained of each designated highway, repeated once an hour over four morning and four evening commuter periods (this means that, altogether, there were 12 morning and 12 evening observations of each highway segment). The morning coverage period was 6:30-9:30 a.m., and the evening period was 4:00-7:00 p.m. Survey flights were conducted on weekdays, excluding Monday mornings, Friday evenings and mornings after holidays. Data were extracted from the aerial photographs to measure average recurring daily traffic conditions by link and by time period (a detailed description of the survey methodology is on the Methodology page).

Survey Data and Deliverables

The three primary products of the aerial traffic surveys are: