Encountered data, statistical ecology, environmental statistics, and weighted distribution methods

Roundabout implementations at traditional intersections have been shown to be effective at reducing severe crashes. Roundabouts have also been implemented at interchange ramp terminals; however, limited research is available. In this study, 25 roundabout ramp terminal implementations were evaluated. The methodological approach consisted of Empirical Bayes for safety effectiveness and crash cost changes, crash type weighted distribution, crash rate analysis of bypass configuration, and cost of implementation. Roundabouts were effective at reducing fatal and injury crashes when replacing existing interchange diamond ramp terminals: 65% reduction for roundabouts replacing stop-controlled ramp terminals and 41% reduction for roundabouts replacing signal-controlled ramp terminals. Observed crash type weighted distributions are provided to visualize the frequency and location of crashes within roundabout ramp terminals for design considerations. Exit ramp and outside crossroad approaches with right-turn bypass showed significantly lower crash rates than designs without bypass. The crash cost analysis showed that roundabouts replacing diamond ramp terminals yielded crash cost savings of between $95,000 and $253,000 per site per year (69% to 54% decrease in crash costs). Considering crash costs savings only, the cost of implementation should be less than $1.9 million for a roundabout replacing a stop-controlled ramp terminal and less than $5.1 million for a roundabout replacing a signal-controlled ramp terminal to accomplish benefit-cost ratios greater than one for a service life cycle of 20 years. Costs are in 2019 dollars.

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The Location Problem of Given and Indivisible Different Units

Environment and Planning A Economy and Space ◽

10.1068/a020341 ◽

1970 ◽

Vol 2 (3) ◽

pp. 341-356

Author(s):

G. Jándy

Keyword(s):

Exact Solution ◽

Heuristic Algorithm ◽

Network Flow ◽

Location Problem ◽

Optimal Solution ◽

Type Problem ◽

Distribution Problem ◽

Enumeration Algorithm ◽

Weighted Distribution ◽

Partial Enumeration

In cases where certain simplifications are allowed, the location optimisation of given and indivisible different economic units may be modelled as a bi-value weighted distribution problem. The paper presents a heuristic algorithm for this network-flow-type problem and also a partial enumeration algorithm for deriving the exact solution. But it is also pointed out that an initial sub-optimal solution can quickly be improved with a derivation on a direct line only, if the exact solution is not absolutely essential. A numerical example is used to illustrate the method of derivation on a direct line starting with an upper bound given by a sub-optimal solution.

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Some observations on fitting assumed diameter distributions to horizontal point sampling data

Canadian Journal of Forest Research ◽

10.1139/x99-169 ◽

2000 ◽

Vol 30 (4) ◽

pp. 521-533 ◽

Cited By ~ 4

Author(s):

Jeffrey H Gove

Keyword(s):

Diameter Distribution ◽

Parameter Estimates ◽

Sample Point ◽

Underlying Distribution ◽

Weighted Distribution ◽

Reliable Parameter ◽

Simulation Results ◽

Larger Sample ◽

Horizontal Point Sampling ◽

Diameter Distributions

This paper revisits the link between assumed diameter distributions arising from horizontal point samples and their unbiased stand-based representation through weighted distribution theory. Examples are presented, which show that the assumption of a common shared parameter set between these two distributional forms, while theoretically valid, may not be reasonable in many operational cases. Simulation results are presented, which relate the conformity (or lack thereof) in these estimates to sampling intensity per point and the underlying shape of the population diameter distribution from which the sample point was drawn. In general, larger sample sizes per point are required to yield reliable parameter estimates than are generally taken for inventory purposes. In addition, a complimentary finding suggests that the more positively skewed the underlying distribution, the more trees per point are required for good parameter estimates.

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