When I learned to drive, cars were pretty easy to understand: they ran on gas, which was fairly cheap, and they had radios.

Other transportation options were limited to boats, buses, trains, planes, and motorcycles. If you lived in a big city, you got around using mass transit and your feet.

Fast forward a few decades and the types of transportation are essentially the same, but the automobile has been radically remade by technology and the auto industry is being roiled by everything from electric vehicles and self-driving cars to ride-hailing services such as Uber and Lyft.

The biggest change to air travel has been the cost, which has come way down since I was 16.

Obviously, I cover transportation and have had a front-row seat for the last decade as a deluge of change has arrived. You might think that if I were to look back, I'd say that the electric car is the biggest change I've seen. Tesla is a $50-billion-market-cap company after all — larger by that measure that Ford and Fiat Chrysler Automobiles!

But you'd be wrong.

Nor is Uber the biggest change I've seen. Nor the advent of high-end luxury air travel, low-cost carriers, or even a rising number of private jets.

High-speed rail? Not so much in the US. Flying cars? Nope.

By far the biggest transportation change I've seen is the explosion in bicycle riding. I lived away from the New York area over a decade ago, and while I rode a bike when I lived in NYC, I was unprepared for the proliferation of bikes on my return.

Bikes, bikes, everywhere

Bike-sharing schemes like CitiBike have two-wheeled conveyances scattered throughout Manhattan. And although everybody in the 1990s got used to dodging bike messengers, nowadays we dodge commuters — or folks who just want to ride across the Brooklyn Bridge. There are bike lanes everywhere — and bike-oriented traffic signals. People ride their bikes year round, rain, shine, sleet, or snow.

I feel as if there are now as many bike shops as there once were Greek coffee shops and dive bars.

This change isn't limited to New York. Cycling has boomed in many other American cities. Whole new genres of bicycles have arrived: bikes with electric-assist motors, bikes with extra carrying capacity (the SUVs of bikes), sleek fixies, fat-tired cruisers, throwback hybrid bikes.

This has quietly become a big deal. Whereas 20 years ago, you took your life into your own hands if you tried to ride from New York's Upper East Side to Midtown, these days a vast flotilla of bikes has been integrated into the city's transportation ecosystem.

"More than three-quarters of a million New Yorkers ride a bike regularly—250,000 more than just five years ago." the NYC Department of Transportation said in its "Cycling in the City" report.

"It is estimated that over 450,000 cycling trips are made each day in New York City—triple the amount taken 15 years ago."

Honestly, I didn't see this coming, but I'm glad it did. Some changes on transportation are disorienting. But this one is welcome.