Currently I have a NEMA 14-30 receptacle for the dryer. I'm wondering is it possible to split one receptacle into 2 NEMA 14-30 receptacles and install a switch to select which receptacle to use when needed?
I need to have an extra jack for my car charger, otherwise I have to unplug the dryer every time I need to charge my car.
You could use a double throw switch.
Other materials required are just commonly available residential wiring supplies. Enclosures or boxes, wire, conduit, etc. Exactly what you use is unique to your situation and difficult to speculate about.
Update: Do note this is not the cheapest of devices. As noted by longneck, running a new circuit may be cheaper. This would be quite true unless the panel is a fair distance from the outlets. Now that we have more detail about the intended use, running a new circuit as suggested by Michael Karas is the only reasonable solution. You do not want to be in a position where you cannot charge your car because you need to dry your clothes, or vice versa. You spent good money on a nice electric vehicle, you deserve to have a proper charging setup for it.
This is so important that in the off chance your service cannot handle the additional load, you should seriously consider what's involved in upgrading the service. There will be additional benefits to this beyond being able to charge your car when you need to.
Electric car chargers require a dedicated branch circuit, as per NEC 625.40:
625.40 Electric Vehicle Branch Circuit. Each outlet installed for the purpose of charging electric vehicles shall be supplied by an individual branch circuit. Each circuit shall have no other outlets.
So, if running another home run to the main panel is not an option, I would simply fit a small spa panel box with two two-pole, 30A breakers and an accessory ground bar in place of the dryer receptacle, with one of them feeding a new dryer receptacle and the other feeding the EVSE (electric car charger). You'll need to make sure the neutrals and grounds are kept separate, with the neutral-bonding screw or strap removed from the panel, by the way, as is necessary for subpanels in this day and age.
The cost of putting in a double-throw switch is probably equivalent to or more than the cost of putting in a dedicated circuit and outlet.
Making your existing dryer circuit switchable is not the best way to address the need for a car charger plug. On top of that by the time you get done purchasing all the materials and and investing in labor to implement the proposed scheme you will likely have spent more money that if you did it the preferrable way.
The better way to do this is to get an experienced person to add another circuit breaker for your power entry panel and run some new wiring circuit to a new plug for the car charger.
The only reasons I can think of for trying the proposed jack switching approach is if there is no way to add an additional breaker to your existing panel or that your existing panel is so under rated that it could not support the an additional circuit. Do note that if your panel is currently full of single wide circuit breakers for lights and outlets it is easy to remidy that situation by replacing those breakers with newer ones that provide support for two circuits per single width location. Replacment of four single circuit single width breakers of the type shown below will open up two adjacent spots needed for your new car charger circuit breaker.
switching 30 A circuits isn't trivial. It would help to know why..
A couple of 30A disconnect switches would be one way..
