The Wheel Shimmy Problem: Its Relationship to Wheel and Road Irregularities

The equations of motion are derived for a single wheel steerable pneumatic tire system. Included in this system are a built-in wheel wobble and wheel-tire irregularities which produce oscillation of the normal load. Special emphasis is placed on the dynamic characterization of the tire cornering force and aligning torque. The results show that the built-in wheel wobble causes a steady shimmy which is large when the wheel rotation frequency is close to the natural shimmy frequency. The results also show that a normal load oscillation which has a frequency approximately twice the natural shimmy frequency causes a decrease in shimmy stability.     

A microeconomic interpretation for the system optimal traffic assignment problem with nonadditive path cost

Using a Bergson–Samuelson welfare function, we outline a microeconomic interpretation of the effects of the non-linearity in the time/cost relationship for travellers in a congested transport network. It is demonstrated that a marginal cost traffic flow assignment following Wardrop's second principle, although it minimizes the total cost of a transport network, may reduce social welfare compared to the market equilibrium assignment based on Wardrop's first principle. A welfare-maximizing assignment model is presented and used to show that if the travellers' utility functions are linear, the assignment that maximizes social welfare will be the same as the assignment that minimizes total network cost, but if users' utility functions are non-linear (reflecting the traditional non-satiation and diminishing marginal utility axioms), the two assignments will be different. It is further shown that the effects of this non-linearity are such that a welfare-maximizing assignment will meet with less user resistance than a minimum total network cost assignment.     

How to Retreat: The Necessary Transition from Buyouts to Leasing

Abstract

Moving assets out of vulnerable areas, known as “retreat,” is a necessary but unpopular option when coastal hazards impact land. Most people prefer protection options. Governments and private land owners tend to adopt a “wait-and-see” approach for retreat. This may be because the time for retreat seems some way off, or because protection has not yet been ruled out, or to avoid unwelcome news. This policy void has allowed people to assume that government will offer to “buyout” property on generous terms after coastal hazards inevitably force the owner to relocate. The problem with that assumption is that (a) it is unaffordable as a solution for all at-risk properties and (b) it acts as an incentive to intensify development in locations vulnerable to coastal hazards. It is, in effect, a form of market distortion which promotes maladaptive behavior. We therefore need to retire that assumption by articulating a standard default arrangement for retreat. This essay suggests that government should establish a default position of renting land, rather than acquiring it, once assets are abandoned by private land owners. This provides sufficient leverage to protect the public interest and a level of financial assistance to the relocating land owner, while allowing markets to properly reflect risk and enabling coastal adaptation.