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Efforts to quantify greenhouse gas emission reduction from the substitution of transit travel for personal vehicle travel now recognize that persons who travel by transit travel fewer miles per day than persons who travel by personal vehicle. In the transit industry the relationship is known as the "land-use multiplier" and among researchers the name "transit leverage" has come into general use. The land-use multiplier is the result of many factors including more efficient land use, which allows shorter trip distances, more walking trips, and trip chaining associated with transit trips. Recognition and confirmation of the land-use multiplier is important in transportation policy development and accurate measurement of the effect is important to specific planning decisions. One cause of the effect allows a test of its scale from existing data. A tenant of travel budget theory is that across populations people travel about the same amount of time every day. The underlying principal is that time, a twenty-four day, is a fixed factor for behavior and the total amount of time in a typical day that can be allowed for traveling is constant across places and historical periods. Given this fixity, if all travelers are using the same travel mode at approximately the same speed, the distance traveled per person per day will be the same across populations. The distance traveled in urbanized areas for person miles in personal roadway vehicles is collected by the Federal Highway Administration annually and the passenger miles traveled on transit in urbanized areas is collected annually by the Federal Transit Administration. These data allow regressions across urbanized areas to verify that the total amount of travel per person is constant across those areas. The resulting regressions are very high with coefficients of determination exceeding 0.94 each year over the past two decades. Travel speed on transit is typically slower than by personal vehicle over entire areas but not necessarily in corridors or otherwise congested areas. The transit travel decision is based on a combination of factors in addition to travel speed including accessibility of destinations, costs, convenience, and the ability to do other activities such as reading while traveling. Since average travel speed, including walking access and egress to the transit stop or station, is at a lower travel speed than the average speed of personal vehicles, an adjustment for that should improve the accuracy of the average travel distance to population regression. Constants are applied to increase the miles traveled on transit to equal an estimate of the miles that would have been traveled if transit riders had driven personal vehicles. As the constant is increased the coefficients of determination also increase, maximizing at values over 0.98 for each year over the past two decades. At the coefficients of determination maximization points the constant, or the number of private vehicle person miles replaced by a single transit passenger mile, ranges from 5 to 7 miles. These values are typically higher than the ratios from most other research because they are a comparison of transit passenger miles to private vehicle person miles while most other studies measure transit passenger miles compared to private vehicle vehicle miles of travel.


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