These costs [of the time used in fastening seat belts] are estimated in the following indirect way because our seat belt use equation does not facilitate a direct calculation of the trade-off between money and time. From a vehicle-type choice model based on the earlier model by Mannering and Winston we find that the marginal rate of substitution between vehicle weight and capital costs is $4.62 a pound. From the seat belt model we find that the marginal rate of substitution between vehicle weight and time to fasten belts is 0.00213 seconds a pound (the same sample was used for the seat belt and vehicle-type choice models). The ratio of these marginal rates of substitution, $4.62 a pound divided by 0.00213 seconds a pound, yields a value of the time to fasten belts over the duration of vehicle ownership of $2,169 a second. Multiplying this by the sample mean time to fasten belts, 2.97 seconds, yields the[total cost]. To the extent that releasing belts takes a perceptible amount of time, this figure understates the total cost of seat belt use.

From: Clifford Winston and Associates. (1987). Blind intersection? Policy and the automobile industry. Washington, D.C.: The Brookings Institution.