In the trucks, James saw 12 * 2 = <<12*2=24>>24 people.
In the buses, he saw 2 * 15 = <<2*15=30>>30 people.
He saw 2 * 2 = <<2*2=4>>4 taxis go past him.
Therefore, he saw 4 * 2 = <<4*2=8>>8 people in the taxis.
In the cars, he saw 30 * 3 = <<30*3=90>>90 people.
Since we know how many vehicles James saw in total, we know that he saw 52 – 12 – 2 – 4 – 30 = <<52-12-2-4-30=4>>4 motorbikes.
So, he saw 4 * 1 = <<4*1=4>>4 people on motorbikes.
He has therefore seen a total of 24 + 30 + 8 + 90 + 4 = <<24+30+8+90+4=156>>156 people.
#### 156