Run-on sentences are very similar to comma splices in that there are two (or more) thoughts put together into a single sentence with no internal punctuation.

• He is a teenager he knows how to use modern technology.
• In many countries public transport is cheap some people still use their own cars.
• Studying online means you can choose your own study times sometimes you need to motivate yourself to study though.

As with comma splices, run-on sentences can be repaired by (a) separating the two thoughts with a full stop (b) using a suitable linking word or (c) using a semi colon. For example:

• He is a teenager. He knows how to use modern technology.
• In many countries, public transport is cheap yet some people still use their own cars.
• Studying online means you can choose your own study times; sometimes you need to motivate yourself to study though.