Well since your question doesn't specify which route 1 I'll give you all route 1 Pokemon with highest chance of appearing region-wise and game-wise:
1.Kanto-
a)Pidgey in R/B/Y
b)Pidgey and Rattata in FR/LG
c)Pidgey in morning and noon and Rattata at night and Hoothoot by headbutting trees in G/S/C in HG/SS
d)Pidgey in grass as while as while flying in Pokemon Let's Go Pikachu and Eevee.
2.Unova-
a)Patrat and Lillipup in normal grass and Herdier in dark grass in B/W
b)Herdier in normal grass and Watchog in dark grass in B2/W2
c)Basculin in water in B/W and B2/W2
3.Kalos-Only first route without any wild Pokemon
4.Alola-With the route being quite big, overall
a)Pikipek and Yungoos in daytime and Alolan Rattata at night in grass in S/M and US/UM
b)Tentacool in water in S/M and US/UM
So yeah if you ever find yourself in a Route 1 in the Pokemon World, the most likely Pokemon to welcome you will be a Pidgey!
Hope I helped:))
