Accessibility (or just access) refers to the ease of reaching goods, services, activities, and destinations, which together are called opportunities.<ref>Accessibility for Transportation Planning: Measuring People’s Ability to Reach Desired Goods and Activities. 27 February 2017. Todd Litman. Victoria Transport Policy Institute. http://www.vtpi.org/access.pdf</ref>
Accessibility almost always measures how long it takes to reach a destinations, or rather how many destinations can be reached within a certain amount of time. However, different tools and evaluations vary in the way they measure first and last mile, the types of destinations they include, population segmentation analysis, and the mechanisms used for counting destinations.
Accessibility analysis measures how long it takes to arrive at certain types of destinations. The most common destination that is measured is jobs. Access to jobs is crucial for employers and employees to maintain a robust economy, and peak commute hours tend to be the most congested times of the week, so increasing accessibility to jobs via transit is particularly important. Data sources for jobs are also easy to acquire through the publicly available LODES and LEHD data.
Other destinations are also often sought out. These can include restaurants, grocery stores, schools, health facilities, parks, etc. Accessibility to these types of amenities has a serious impact on quality of life, and is therefore important in evaluating transit effects on a community. Also, since only 20% of trips are for a home-to-work commute<ref>Commuting in America 2013: The National Report on Commuting Patterns and Trends. American Association of State Highway and Transportation Officials. http://traveltrends.transportation.org/Pages/default.aspx</ref>, factoring in other trip destinations has a big impact on how much people will use a transit system. There are no government generated sources for these databases. Some tools use open source options, such as [[OpenstreetMap]], while other acquire proprietary databases. A challenge when working with other destinations is how to group them or weight them. Analyzing accessibility to grocery stores might be relatively easy (although even in this example, classifying grocery stores might be difficult). However, analyzing accessibility to amenities broadly raises questions of which amenities count and which amenities are most important.
*[[Transport Analyst]] offered by [[Conveyal]] is an open source tool. It offers accessibility information for various cut-off points and creates spectrograms that show the change in accessibility as travel time increases, but does not create a related score. Analyst offers accessibility measures for a number of different destination types, acquired from [[OpenStreetMap]], and allows for demographic overlays.
*[[TBEST]] is a tool mostly used for estimating transit boardings that was developed by [http://www.fdot.gov/ FDOT]. TBEST includes an accessibility analysis function, but it is limited in destination options, and only calculates stop to stop travel times.