Travel time variability may significantly influence a driver's route choice. Urban infrastructure managers are interested in reliable estimation of travel time, which could provide better information to drivers, encourage reassignment on the network, and optimize use of the network. This study addresses arterials in undersaturated conditions with known fixed-time traffic signals. The kinematic wave model was chosen to represent traffic dynamics simply. A semianalytical (grid-free) method is applied to determine the separation between vehicle groups at each signal of the arterial. The main contribution of this paper is an aggregated diagram that describes the functioning of this arterial. The aggregated diagram graphically provides a direct assessment of vehicle travel times with respect to their departure and traffic flow. This tool depends only on signal settings and is cyclic and invariant for fixed-time signals. The diagram can be used to generate probabilistic travel time distributions when some input parameters are uncertain. The diagram appears to offer insight when traffic flow is not accurately known.