I think the biggest plausible change to reality you could engineer is a difference in the development of energy production technology to remove oil and natural gas as fuel options. Your alternate-reality 1990s society developed through an Industrial Revolution in which liquid fossil fuels were never tapped on a wide scale as a source of energy; humans transitioned from wood and coal into more sustainable sources like hydroelectric, nuclear and solar without the oil step in between.
How did that happen? That's your problem to solve. Maybe the first wells that would have been commercially exploited in our own reality instead exploded into massive infernos, killing thousands, poisoning nearby waterways and leading to an international moratorium on oil drilling, much as various nuclear accidents have muted the conversation of ramping up nuclear energy as a substitute for fossil fuel use in grid electricity in our own reality. Coal mining is still tolerated, but the world's growing energy needs led to more widespread adoption of nuclear plants, perhaps despite Three Mile Island or even Chernobyl. To store and mobilize electrical power, battery technology was also accelerated, so your 90s-era society, instead of still using toxic and relatively less dense nickel-cadmium chemistry, discovered and commercialized lighter and denser lithium-ion chemistries on an accelerated timeline.
The lack of oil to replace coal- and wood-burning rail engines required a rail technology powered by grid electricity, thus prompting Eisenhower to build a highly-connected, Federally-funded high-speed rail network, co-opting private and/or State ownership of the existing railroad. Rail, not roads, became the primary transportation grid of the United States (and of many other countries besides), and what road vehicles do exist are battery-powered short-range vehicles, designed for use in "park-and-ride" commutes to drive a few miles to the nearest mass transit station and catch one of the trains running every five minutes along routes closely mirroring major highway networks in and between major cities. Anywhere you want to go, a train will take you, unlike the situation in most of the US's major cities.
However, without petroleum, the energy requirements for a practical commercial aircraft just don't exist. The energy density of even modern batteries can't even be accurately plotted on linear-scale energy density graphs that include fossil fuels and hydrogen. So, while knowledge of the fundamentals of flight are still commonplace, the taboo of oil use stunted the development of powerplants that were small, light, powerful and reliable enough for meaningful flights of large-scale aircraft. Ultralights that run on batteries or wing-incorporated solar panels are toys for the rich (much as they are now), but by this alt-1990s timeline, we never solved the problem of how to get enough energy density into the air with a required level of safety and reliability (nuclear planes were looked at for all of 5 minutes before someone asked what would happen when one crashed in a populated area), and so commercial air travel never developed to supplant rail and ship travel as the fastest, safest way to move humans over long distances.