Step 1: Influence of Modal Alternatives.
\nTravel demand forecasting accounts for various transport modes (e.g., private vehicles, public transit like buses and metro, and non-motorized options). The introduction of new modes or enhancements to public transportation in the target year will alter travel demand distribution. \n\[\n\Rightarrow \text{Hence, statement (P) is correct.}\n\] \n\n
Step 2: Impact of Population.
\nProjected population in the target year is the primary driver of travel demand. An increased population directly correlates with a higher number of trips and consequently, greater travel demand. \n\[\n\Rightarrow \text{Hence, statement (Q) is correct.}\n\] \n\n
Step 3: Effect of Land Use.
\nThe distribution of land use (residential, commercial, industrial) significantly impacts trip generation and attraction. For instance, a higher concentration of commercial zones will result in more work-related trips. \n\[\n\Rightarrow \text{Hence, statement (R) is correct.}\n\] \n\n \nTherefore, all three factors P, Q, and R are influential in predicting travel demand. \n\n \n\[\n\boxed{\text{P, Q, and R are all correct}}\n\]