Future BTS, monorail and MRT lines in Bangkok mean developers are starting to buy up land near proposed lines and building condos.
The green line extension and new pink line are prime examples of how you can find new properties in locations where there will be new lines. These properties will provide transport convenience but are still considerably cheaper than condos along the current BTS / MRT lines. One thing to note is that these proposed lines will take a minimum of three years to be built, so if you buy now, you will have to make do with other transport forms. Although most of them are scheduled to complete within 2021, it is better to wait for official government announcements rather than just relying on hearsay about proposed lines.
There are plans for improved public transport such as monorails in Phuket and Chiang Mai. These mean that traveling in these areas will improve and could lead to an increase in condo developments and sales.
https://www.expatden.com/thailand/buying-a-condo-in-thailand/#:~:text=All%20money%20for%20the%20purchase,governed%20by%20the%20condominium%20act.