The correct answer is option 2.

The first statement says that roads in Harappan cities were not always straight and did not always cross each other at right angles. This statement is correct. Archaeological evidence suggests that the streets in Harappan cities were not straight. They had curves and bends, possibly due to the presence of pre-existing structures or natural landscape features.

The second statement says that there was uniformity in the average size of bricks for houses and city walls in Harappan cities. This statement is also correct. Excavations at Harappan sites have revealed that bricks of a standard size were used in the construction of houses and city walls. This standardized brick size points towards a centralized authority and a planned approach to city construction.

In conclusion, both statements in the question are correct, and the answer is option 2 - 2 only.