Review of AREMA formula for allowable speed on a curve

Abstract: There exists a universally accepted equilibrium superelevation formula to compute speed on a curve. The AREMA modified the universally accepted equilibrium superelevation formula by subtracting vehicle roll from the unbalanced superelevation to reduce speed; this is not acceptable theoretically. The problem lies to realize the fact that the sum of actual and unbalanced superelevation is same whether it is computed on the track plane or on car floor plane. The other problem lies in the lack of understanding to distinguish between the axle based unbalanced superelevation (or lateral acceleration) and perceived unbalanced superelevation (or lateral acceleration); this leads the AREMA to equate the axle based unbalanced superelevation with the comfort limit which is supposed to be interpreted as the perceived value. Thus, the perceived value should be equated with the comfort limit. This paper discusses the other deficiencies e.g., flat value of roll etc. of the modified equilibrium superelevation formula by AREMA. The paper suggests keeping the universally accepted equilibrium superelevation formula as it is and a method to take care of vehicle roll effect in a theoretically acceptable way by taking suspension factor of a vehicle into account. In absence of suspension factor value from supplier of vehicle, the paper suggests lean test. Finally, the paper suggests formula to compute speed on a curve that takes care of roll effect in an acceptable way.