Parking at the airport

At the Delhi airport parking you pick up a ticket on your way in from an automatic dispenser, pay and then insert into an automatic reader on the way out within 15 minutes of the payment. Parking charges are in three buckets: 0-30 minutes, 30 minutes to 2 hours and then full day charge. All parts except the ‘pay’ one are automated. They perhaps avoided automating it for the cost of interchange. Also I don’t like it because it creates a wait for a bit too long and would only get worse when lots of people get out together from arrivals (3 am on any given day is perhaps the busiest at DEL).

Anyway, I am writing today about something else. The ’15 minute’ part. Once paid, a new ticket is printed and provisioned to work for the next 15 minutes – which leaves enough time for people to find their cars and leave.

I think however that this (15 minute constraint) is unnecessary and easily avoidable at no extra cost. My impulse to think about this came from the long wait I have to do when I have some luggage with me and want to quickly head back to my car and to my way home ASAP. If only they allowed people to pre-pay their parking fee, it would be so much better. The benefit of removing the 15 minute constraint would be that the queue on the human-powered pay counter would drastically reduce because people can pay any time between entry and exit.

Here is how:
The printed ticket is a bar coded paper card that is machine readable and carries 20 digits. Right now it carries a unique number that is allowed to open the gates for the next 15 minutes after which it expires. These systems are pretty similar to prepaid calling cards and recharge cards that telecom operators have used since eons. They are primarily designed to avoid fraud so nobody can print them at home.

Instead, these twenty digits could be split into two: one part the expiry date+time and the second part a unique number that ensures it is protected from fraud. This combination of expiry time and the unique number could further be encrypted so it isn’t easy for anybody to predictably print new ones.

Do you reduce the security by now using lesser number of digits than before for the unique number ? Yes 12 digit uniques are less secure than 20 digit ones but by a practically irrelevant amount. Moreover the combination of these two parts can also be jumbled together to raise security even further.

Now the automated reader at the exit would know to look for a valid expiry time along with a check to make sure it is not a fraudulent ticket.

The change required is purely in software which is the kind of change I always consider equal to buying real estate. Done right, it is one-time investment that never stops giving returns.

The benefit would be a lesser queue and possibly lesser people required at the pay counter. Happy passengers, happy car-parkers, happy pay counter staff. It is truly a situation where the total amount of happiness in this universe will increase.