Complex sentence: The nearest vehicle alternatives are the Blackwall Tunnel about upstream to the west, or the Dartford Crossing around downstream to the east; but both tunnels have height restrictions for heavy goods vehicles, and users of the Dartford Crossing incur toll charges.
Split into simpler sentences: The nearest vehicle alternatives are the Blackwall Tunnel about upstream to the west, or the Dartford Crossing around downstream to the east. Both tunnels have height restrictions for heavy goods vehicles, and users of the Dartford Crossing incur toll charges.