1. Separate an app estimate from your arrival deadline

Work backward from when you must reach your desk or appointment location. Include leaving home, walking to a stop, waiting and transfers, parking, and entering the building in your record. Check whether the app estimate includes those stages before comparing it with your own journey.

For several trips, note departure and arrival times and reasons for delay, comparing similar days and time periods. “Twelve extra minutes after a missed connection” helps you decide whether to change departure time or route more than “usually forty minutes.” A short personal log is a starting point for adjustment, not data that guarantees 95% on-time arrival.

2. A 25% buffer can be a calculation, not a recommendation

FHWA's travel time reliability guidance distinguishes average travel time from travel time on high-delay days. Its buffer index is '(95th-percentile travel time − average travel time) ÷ average travel time.' The 95th percentile means approximately 95% of the times in that dataset are at or below that value.

Suppose a hypothetical dataset has a forty-minute average and a fifty-minute 95th percentile. Buffer time is 50−40=10 minutes and the buffer index is 10÷40=25%, giving fifty minutes to plan in this example. That 25% is not a fixed allowance for every commuter, and these numbers are not measurements from a real route. If the measured journey excludes movement inside the building, include that time separately.

3. Adapt for transfers and important appointments

A missed transit connection may add the wait for the next service. Check whether the app's fast route depends on a transfer you would have to run to make, and select connections that fit your walking pace and access needs. Look up the next service or an alternative route you could use if you miss it.

For an important booking, include check-in time and prepare a way to contact the destination if you expect to be late. Review both excessively early and late arrivals instead of continually increasing the allowance. You can choose a less tiring route, but this planning method does not guarantee reduced stress or greater happiness.

On days with weather problems, incidents or closures, check transport operators and local authorities rather than relying only on usual trip records. Extra time cannot make an unsafe route safe. US NWS flood safety guidance warns against driving or walking into flood water. Consider another route or postponing the trip when conditions are dangerous, and follow local instructions.

4. Sources

  • FHWA: Travel Time Reliability — definitions of average, 95th percentile, buffer time and buffer index. Forty and fifty minutes are a separate hypothetical example here.
  • NWS: Turn Around Don’t Drown — safety boundary for flooded roads and walking routes.