In today's world where everything has to be fast — from under 10-minute groceries, 30-second videos to fashion trends lasting weeks — the idea of travel delays seems almost antithetical. But congestion has become so ingrained in our daily routines that perception of mobility has evolved to accept it as “inescapable” rather than “contradiction.”
New Delhi-based non-profit Centre for Science and Environment (CSE) surveyed car commuters in Delhi to understand their perception of travel time. Turned out, cars move slower on average in Delhi than the average speed of a cyclist!
Respondents were asked to estimate the time and distance taken for their daily journey. Travel time per kilometre, based on the responses, ranged from 1.5-8 minutes per kilometre, averaging at 2.79 minutes per kilometre. This means an average travel speed of 21.5 kilometre per hour (kmph), which is lower than the average speed of a cyclist (15 to 25 kmph depending on the rider’s proficiency and type of cycling).
It must be noted that the sample population was chosen at random, and responses were collected anonymously via a questionnaire survey circulated online across Delhi commuters to eliminate the geographic bias.
Interestingly, the travel time quoted by respondents was for the peak hours of travel (when congestion is at its peak) without the survey mentioning the time of the day.
Speed change during different times of day in Delhi, September 10-16, 2024
There is one seemingly obvious explanation: The survey asked for the commuters’ daily journey, which refers to 'primary trips' that are made usually made during peak hours.
But there was another factor at play: Human memory and experience. More specifically, a psychological bias governs this perception, which is called the “peak-end rule” in this context. According to the rule, people judge an experience based on how they felt it at its peak and end, rather than the average of every moment.
In the case of commuting, peak-hour delays often represent the most frustrating and intense moments, so they are more likely to be recalled when commuters think about their travel times. This explains why commuters almost always mention peak-hour travel times when asked about their journeys.
However, just as congestion is higher during specific times of day, this warped perception of travel also has adapted to the time of day. Metrics have been designed to quantify the perception of congestion and travel reliability which can reflect on how much impact they can have on future expectations and behaviour of commuters.
Two prominent quantifying indices are 'travel time index' (TTI) and 'planning time index' (PTI). TTI is the additional time commuters spend travelling during peak hours, while PTI reflects the time buffer commuters need to add to ensure timely arrival at their destinations, given the unpredictability of traffic.
If TTI is equal to 1.5, the trip will take 50 per cent longer than in congestion-free conditions. PTI uses the 95th percentile speed (for a period) on a route at any given time-of-day, to ensure on-time arrival 95 per cent of the time. Therefore, for instance if PTI is equal to 2, commuters need to plan for double the free-flow time to avoid being late 95 per cent of the time at that hour of day.
When plotted together for all hours of the day, the buffer region between travel time index and planning time index is the “reliability buffer”, that is the buffer required to ensure reliable time compared to average travel time.
In another CSE study, TTI and PTI were calculated for 25 major routes, including entry and exits for NCR districts, for a period of one regular work-week (September 10-16, 2024). It was found that PTI can go as high as 7.7 during evening peaks, which means travelling on those stretches will require a time buffer seven times higher than the free flow.
Evening peaks are observed to have greater variability in travel time prediction. In the morning, travel is often more spread out as people start their commutes at slightly different times depending on their personal schedules but most people finish around the same time in the evening.
Average planning time index and travel time index during different times of the day in Delhi
Additionally, evening trips are not only limited to primary trips. Secondary trips such as running errands, shopping, social visits and so on add to the trip load. Further, evening trips can be shorter, which can lead to commuters preferring personal modes more than public transport.
The reliability buffer peaks at 7pm, with an average PTI of 3.6 and average TTI of 2.7. In simpler terms, during this hour, a 10-minute journey (without traffic) will end up taking 27 minutes, and will require a buffer of nine more minutes due to unreliability. Therefore, the commuter will plan to leave atleast 36 minutes prior.
This extra planning time is a sobering reminder of the subtle acceptance of congestion as part of daily routine. Perhaps the real question isn’t how we endure congestion but why we continue to accept it.
Normalising congestion obfuscates the environmental and economic costs of associated with it in the minds of the commuters. This impedes the necessary shift away from private transport to cleaner modes such as mass transit.