Accessibility, the number of time-decayed jobs available to each zone within a region, can help prioritize candidate transportation investments. This paper demonstrates how to compute auto accessibility using commonly available resources and identifies strategies needed to render calculations feasible and transparent. (The scope excludes transit and pedestrian impacts.)

For the first objective, computational solutions included developing a semi-automated method to import legacy transportation networks, automating turn prohibitions, and using an algorithm to check for inconsistently formed service areas that sometimes occur in a random fashion with geographic information system software. Failure to exercise quality control using these approaches gives erroneous results: not solving the problem of inconsistently formed service areas led to a region within 50 mi of a 1-mi corridor (where improvements are proposed) having an accessibility almost 40 times higher than the correct value. For the second objective, the influence area (i.e., catchment radius) mattered most: for one project, the forecast accessibility improvement dropped by 80% when an area within 45 mi of the project, rather than an area within 15 mi, was the basis of the analysis. Other decisions affected forecast accessibility improvement less: the choice of the number of centroid connectors affected forecasts by an average of 23% (with a 10-mi influence area). Choosing to eliminate negative net accessibility contributions, attributed to geometric approximations in the software, affected forecasts by less than 21% (35-mi influence area or smaller). Ranking five proposed investments in relation to their forecast accessibility benefit demonstrated the importance of documenting users’ computational choices.

可访问性，即一个地区内每个区域可用的时间衰减工作的数量，可以帮助优先考虑候选交通投资。本文演示了如何使用常用资源计算自动可访问性，并确定使计算变得可行和透明所需的策略。（范围不包括交通和行人影响。）

对于第一个目标，计算解决方案包括开发一种半自动方法来导入传统交通网络、自动禁止转弯，以及使用算法检查有时以随机方式出现的地理信息系统软件的不一致形成的服务区。未能使用这些方法进行质量控制会产生错误的结果：不解决形成不一致的服务区问题导致 1 英里走廊（建议改进的地方）50 英里内的区域的可达性比正确的高出近 40 倍价值。对于第二个目标，影响区域（即集水半径）最重要：对于一个项目，当项目 45 英里内的区域而不是 15 英里内的区域时，预测可达性改进下降了 80%，是分析的基础。其他决定对预测可访问性改进的影响较小：质心连接器数量的选择对预测的影响平均为 23%（影响区域为 10 英里）。选择消除归因于软件中几何近似的负净可达性贡献，影响预测不到 21%（35 英里的影响区域或更小）。排名五个与其预测的可访问性收益相关的拟议投资表明记录用户的计算选择的重要性。归因于软件中的几何近似，影响预测不到 21%（35 英里的影响区域或更小）。排名五个与其预测的可访问性收益相关的拟议投资表明记录用户的计算选择的重要性。归因于软件中的几何近似，影响预测不到 21%（35 英里的影响区域或更小）。排名五个与其预测的可访问性收益相关的拟议投资表明记录用户的计算选择的重要性。