INTERMODAL IMPACTS: INTERSTATE HIGHWAYS AND AIRPORT VIABILITY
The author examines the impact of individual interstate highway projects on airport viability in the State of Indiana from 1957 to 1970. The airports considered are or have been terminals for major trunk and local service air carriers since 1957. The total number of passengers carrier by air is taken as the measure of airport activity and viability. A multivariate time series methodology was used. It was found than the construction of new roads, which increases accessibility, is beneficial to larger airports but detrimental to the smaller local-service airports. /TRRL/
The Effect of the Interstate System on Short-Haul Air Passenger Demand
When an interstate highway is completed between two cities less than 200 miles apart, some people find it more convenient to switch from air travel between the two cities to automobile or bus travel. This paper employs a multiple regression model to quantitively examine this effect of interstate highway construction on short-haul air market. Several techniques are used to isolate the impact of changing highway quality on the short-haul air market from a myriad of other influencing factors. The city-pairs chosen for the regression sample are all between 105 and 185 miles apart so that the distance variable is constrained. An “airport use” variable is introduced to reflect changing environmental demand determinants such as income and population. The regression is run in first difference form, which eliminates multi-collinearities as well as the influence of static factors. Finally, quarterly data is used rather than yearly data to provide more degrees of freedom, and quarters are compared with the same quarters in an earlier year to eliminate the effect of seasonal variations. The coefficients of the resulting regression indicate two important conclusions. First, short-haul air markets are growing only about half as fast as the air market as a whole. Second, a significant number of travelers do switch from airplane travel to automobile travel when an interstate highway is made available for a one hundred to two hundred mile trip.
THE PERFORMANCE OF STEADY DETONATION ENGINES
Propulsion systems driven by steady normal detonations are studied. The practical di‐culties associated with stabilizing a detonation wave are highlighted. The requirement on the freestream total enthalpy is considered in parallel with efiects such as condensation or auto-ignition of the fuel-air mixture and limitations associated with fuel sensitivity to detonation. A criterion for detonation stabilization is formulated and applied to an analytical treatment of a detonation ramjet and a detonation turbojet, which are the respective analogs of the ramjet and the turbojet using detonative combustion. The performance of these engines is evaluated and compared to the ideal ramjet and turbojet models for hydrogen and JP10. A limitation is placed on the maximum total temperature allowed in the combustor, based on material considerations. The results show that steady detonation engines have a small thrust-producing range, due to the requirements for detonation stabilization. Their performance is always lower than that of the conventional ramjet and turbojet because of the total pressure loss across the detonation.