For the believer, there are sins that do not lead unto death and sins that do lead unto death (See 1 John 5:16-18). Paul lists those sins several times that lead unto death in Galatians 5:19-21, Ephesians 5:3-5, 1 Corinthians 6:9-10, Colossians 3:5-7, Romans 1:28-32. John also lists certain sins that will lead a person unto the "Second Death" or the Lake of Fire. For John says that any man who hates his brother is a murderer, and we know no murderer has eternal life abiding in them (1 John 3:15).
Sins that do not lead unto death are hidden or secret faults Psalm 19:12 or confessed sin (See 1 John 1:2, 1 John 1:9, Luke 18:9-14). But no, a believer is not going to Hell if they happen to break the speed limit. However, if they murder someone, then they are committing that type of sin that leads unto death and it needs to be repented of (Because it is a serious sin that will lead unto death). In fact, we know not all sin is the same because there are some sins that cannot be forgiven (Like speaking bad against the Holy Spirit, committing suicide, and rejecting Jesus while having the Spirit (i.e. apostasy).