Is it permissible to combine prayers when travelling by car for several hours?

Short answer

Yes, it is permissible to combine Dhuhr with Asr and Maghrib with Isha during your journey. The method of transport does not affect the ruling as long as the minimum travel distance (~77 km) is met.

Evidence

Ibn Abbas reported that the Prophet combined prayers during travel (Muslim, 705). Karachi to Lahore far exceeds the minimum distance.

Types of combination

Jam al-taqdeem: pray the later salah at the earlier time. Jam al-takheer: pray the earlier salah at the later time. Both are valid. You may also shorten four-rakah prayers to two.