On the ratios of urban mobility, Part 1: the HoTer model of travel demand and network flows
Abstract
Mobility systems in urbanized territories have been featured out in Travel Demand Models by state variables of land-use occupation, trip generation, trip distribution, modal split and network assignment, with emphasis on causal relationships between the variables and on spatial detail for each kind of variables. The article is aimed to provide notional averages, say ratios, for each kind of variables, and to state the causal relationships between the variables as simple analytical formulas between the ratios. This is achieved by going along the classical four steps of travel demand modeling, in a theoretical way for an idealized territory satisfying three postulates of homogeneity: namely, at block level, at link level and of indefinite spatial extension. The said formulas constitute rules of thumb linking the mobility ratios of spatial density of human occupation, trip emission rates, average trip lengths, modal shares, generalized trip cost per length unit, together with traffic variables of speed, flow rate and vehicular density at the link level. The model is stated in eight steps, namely (i) territorial composition, (ii) trip generation, (iii) trip lengths and traffic formation, (iv) quality of service, (v) trip distribution using a gravity model, (vi) modal split by multinomial logit, (vii) traffic laws, (viii) traffic equilibrium. It is followed by a Discussion of the model outreach and limitations. Areas of further research include traffic laws, impact assessment and economic analysis.
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