→Decay: small correction
[[File:Decay function.png|thumb|A decay function showing the change in weighted values for different modes and destination as travel time increases<ref>"Operationalizing Accessibility: Tools and Practices." State Smart Transportation Initiative. 30 March 2017. http://www.ssti.us/Events/operationalizing-accessibility-part-1-tools-and-practices/</ref>]]
Decay functions offer a more fine-tuned assessment of accessibility by weighting destinations based on how far away they are. A job that is five minutes away contributes more to accessibility than one that is thirty minutes away, and a job that is thirty minutes away contributes about the same as one that is thirty-one minutes away. Decay functions usually have a cut-off, somewhere around the 60 or 90 minute mark, where destinations are considered so inaccessible that they can no longer greatly contribute.
Using decay is challenging for a number of reasons. A meaningful and reliable decay function has to be developed. The computation effort of calculating the exact distance to each location and weighting the location is large and complicated. Finally, because location are weighted, the final output is unit less; it cannot be explained as number of jobs within 30 travel time. This may allow for internal comparisons but may be difficult to understand conceptually for public presentations. One solution to improve presentation is developing a clear scale and creating references are explanations for various points on the scale. (ex. a 1-100, where 80-100 is excellent accessibility, etc.)
==First and Last Mile==