what are transportation barriers

Please clarify your question. Are you asking about barriers to transportation in general -- major rivers, steep mountains, etc.? Or are you asking about transportation barriers for handicapped people?

Your question is unclear. There are many different types of transportation barriers. However, even though this is not my area of expertise, I searched Google under the key words "transportation barriers" to get these possible sources:

http://www.alltheindustrials.com/search.aspx?q=Barriers&rd=1&brand=
http://www.access-board.gov/recreation/final.htm
http://www.uwm.edu/Dept/ETI/dot.htm
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http://repositories.cdlib.org/lewis/cspp/05/

I hopes this helps. Thanks for asking.

there too stop people that are not aloud in and out of the country going in and out of the country

The transportation barriers you are referring to are typically known as immigration or border control barriers. These are measures put in place by countries to regulate the movement of people across their borders. These barriers are established to ensure national security, control immigration levels, protect domestic job markets, and prevent illegal activities.

To get more information about specific transportation barriers related to immigration and border control, you can start by conducting a search on reliable sources such as government websites, news outlets, or international organizations. These sources often provide detailed information about immigration policies, visa requirements, border crossings, and the procedures involved.

You can also refer to official government websites of specific countries you are interested in to learn about their immigration policies and any transportation barriers they may have in place. These websites usually provide information on visa applications, entry requirements, and border control procedures.

It's important to note that immigration and border control policies vary from country to country, and they can change over time. Therefore, it is essential to consult up-to-date and reliable sources for accurate information.