One of the more popular assertions in California's current debate over traffic congestion is that road building is not keeping pace with California's booming population. A recent report to the legislature from the California Transportation Commission detailed the problem of playing catch up with "three decades of population growth that out-paced highway and road capacity increases by a factor of two, and growth in vehicle miles of travel (VMT) that out-paced population by a factor of nearly three." Similar reports about highways failing to keep pace with population have been widely circulated in the state legislature and the media. Recent articles and reports have variously asserted that population has doubled while the state highway system has grown by less than ten percent in the last two decades. Other reports claim that California's highway system has grown by only 64 lane-miles the last two decades.

Have highways really failed to keep pace with population and the amount people drive? And is a comparison of highway and road expansion with population growth and vehicle miles traveled even a meaningful measure of transportation success or failure?

Overall Growth in the State's Road Network. In the thirteen years between 1984 and 1997, at least 26,000 lane-miles of streets and highways were added to the entire road network statewide. The Interstate highway system grew by five percent, freeways and expressways off the Interstate system increased by 26 percent, principal arterial streets grew 13 percent, and minor arterial streets increased 26 percent. Over that same period California's population grew 28 percent and the amount of driving increased by 45 percent.

TRENDS IN STATEWIDE ROAD SUPPLY AND TRAFFIC DEMAND
Facility Type	1984	1997	Percent Change 1984-97
Interstate Highways	13,584	14,276	+5%
Other Freeways & Expressways	6,252	7,873	+26%
Principal Arterial Streets	28,851	32,618	+13%
Minor Arterial Streets	35,240	44,472	+26%
Collector Streets	61,976	66,602	+7%
Local Streets	?	215,989	?
TOTAL STATEWIDE	?	381,827	?
Subtotal less Local Streets	194,590	220,608	+13%
Population (millions)	25.8	32.9	+28%
Vehicle Miles Traveled (billions)	196	286	+45%
source: California Research Bureau; Federal Highway Administration; California Department of Transportation.

Of course, expanded facilities were built in many different parts of the state, but with only statewide figures, it's difficult to tell how those expansions compared with population growth in the same area, making drawing more detailed conclusions difficult. However, there are more disaggregated statistics available.

Road Expansion in Metropolitan Areas. A vast majority of California's population lives in metropolitan areas - geographic regions defined by the U.S. Census consisting of both cities and suburbs. Nearly all of California's traffic congestion problems occur in its metropolitan areas, and for this reason many respected transportation research organizations like the Texas Transportation Institute conduct their analyses of traffic congestion at the metropolitan level rather than the state level.

When analyzed at the metropolitan level, the major roadway network's capacity in California's largest urbanized areas grew 24 percent between 1984 and 1997 (the most recent year for which metro area level data is available), while population grew by 28 percent and the amount of driving increased 45 percent. Thus, in California's major metropolitan areas, roadway capacity did indeed increase in roughly the same proportion as population in terms of percentage growth since 1984. But more importantly, what did outpace both population and highway growth at both the regional level and statewide was the total growth in driving measure in vehicle miles traveled (VMT).

TRENDS IN REGIONAL ROAD SUPPLY AND TRAFFIC DEMAND
ITEM	1984	1997	Percent Change
Metropolitan Freeways, Expressways & Principal Arterial Streets (lane-miles)	27,990	34,570	+24%
Metro Area Population (millions)	18.8	23.9	+28%
Metro Area Vehicle Miles Traveled (billions)	94	137	+45%

Simply measuring the increase in available roadway space in terms of its length (by the number of miles) and its width (by the number of lanes, so that the combined measure produces total "lane-miles") is no longer viewed as the best gauge of the true overall capacity of a road network to handle traffic. Contra Costa County recently completed a multi-billion project to reconfigure the Interstate 680 and state highway 24 interchange to increase the capacity of the two highways to handle traffic flow without adding any new significant increases in the number of total lane-miles. A highway construction project in Cincinnati, Ohio, will actually decrease the number of lanes in a massive interchange between several highways near downtown, while at the same time increasing the ability of the interchange to handle traffic through a more efficient design.

The Need for Better Performance Measures

Comparing population or the increase in driving with roadway capacity growth may not necessarily answer the question as to how much expansion the transportation system needs, especially since lane-mile increases may not take into account efficiency measures that improve the capacity a given facility. In addition, measures of congestion vary widely, making assessment of problems difficult.

More sophisticated measures of roadway supply and traffic demand are obviously needed. Agencies should agree on common measures and indicators of congestion that can be produced, published and monitored on a regular basis. State, regional and local transportation agencies need to track and publicize better data on the overall capacity of streets and highways that incorporate ongoing efforts to improve traffic flow through maximizing efficiency and operations.